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      01-25-2013, 05:48 PM   #1
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Need Help Please - Ground Loop?

Hello all, I am in desperate need of some help. Back in July I bought a 2011 E90 with 5800 miles on it. A few months ago, I noticed a very high-pitched noise in the cabin when driving. Here is what I know.

- Was not there when I bought the car
- Only changes has been PPK Stage 1
- Noticed noise at around 9K miles, now at 15k
- Noise only happens when the engine is on
- Noise varies with engine speed
- It is very noticeable, when I first start the car. I can hear it change pitch until the engine settles at idle and then it is a constant noise.
- The noise is VERY soft
- I have not touched anything with the electronics, radio, engine, anything

Brought the car into my dealer:
- They said the confirmed the noise
- Replaced the "radio" and re-coded the radio to the car
- Picked the car up today, and guess what, noise is still there!
- Met with the techs, and naturally NOBODY can hear the noise.
- Dealer does not know what to do, but they are being very helpful and really care. But they do not know where to look.

My assumption is the noise is coming from the stereo, it is almost impossible to tell. Does anybody here have any experience with anything like this? My thoughts are it is a ground loop or a bad amp. I just checked the amp, but, it seems to not be grounded. Anybody know where the ground is so I can check it? Any other grounds I should check?

Any help here would really be appreciated, I fear I will never figure this out and be forced to sell the car. The noise is driving me nuts!
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      01-25-2013, 06:38 PM   #2
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Quote:
Originally Posted by ry335 View Post
Hello all, I am in desperate need of some help. Back in July I bought a 2011 E90 with 5800 miles on it. A few months ago, I noticed a very high-pitched noise in the cabin when driving. Here is what I know.

- Was not there when I bought the car
- Only changes has been PPK Stage 1
- Noticed noise at around 9K miles, now at 15k
- Noise only happens when the engine is on
- Noise varies with engine speed
- It is very noticeable, when I first start the car. I can hear it change pitch until the engine settles at idle and then it is a constant noise.
- The noise is VERY soft
- I have not touched anything with the electronics, radio, engine, anything

Brought the car into my dealer:
- They said the confirmed the noise
- Replaced the "radio" and re-coded the radio to the car
- Picked the car up today, and guess what, noise is still there!
- Met with the techs, and naturally NOBODY can hear the noise.
- Dealer does not know what to do, but they are being very helpful and really care. But they do not know where to look.

My assumption is the noise is coming from the stereo, it is almost impossible to tell. Does anybody here have any experience with anything like this? My thoughts are it is a ground loop or a bad amp. I just checked the amp, but, it seems to not be grounded. Anybody know where the ground is so I can check it? Any other grounds I should check?

Any help here would really be appreciated, I fear I will never figure this out and be forced to sell the car. The noise is driving me nuts!
If I'm not mistaken I believe the HiFi and Logic 7 amps are grounded on top of the rear left fender well. You can check the ground there but you'll have to remove the panel to gain access.

Since there seem to be no mods that can affect the OEM audio system I would agree that it is either a grounding issue or a bad amp, but I am not exactly the expert on that. Technic and VP Electricity may be able to add to what I said.

I do think however that you need to let the dealer take care of this, and doing your own troubleshooting should really be the last resort!
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      01-25-2013, 07:44 PM   #3
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Production date and type of audio system, please?
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      01-25-2013, 09:41 PM   #4
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Quote:
Originally Posted by Technic View Post
Production date and type of audio system, please?
Hi-Fi, 04/11.
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      01-25-2013, 10:58 PM   #5
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Quote:
Originally Posted by ry335 View Post
Hi-Fi, 04/11.
Why the OEM amp was not replaced?
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      01-25-2013, 11:49 PM   #6
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Can you make a recording and post it?

Can you make a recording and post it?
Is it white noise ?
Have them Disconnect the amp and see if the noise still is there.
Or is the noise still there with the stereo off as the amp is on
anyway I think.
Or is it one of those 2011's that didn't get a Hi Fi system?
Do you have tweeters in the door sails?
The production date would indicate is has Hi Fi.

Last edited by ctuna; 01-25-2013 at 11:57 PM.
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      01-26-2013, 09:01 AM   #7
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Quote:
Originally Posted by Technic
Quote:
Originally Posted by ry335 View Post
Hi-Fi, 04/11.
Why the OEM amp was not replaced?
I assume it was not, they said they just replaced the "radio".
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      01-26-2013, 09:03 AM   #8
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Quote:
Originally Posted by ctuna
Can you make a recording and post it?
Is it white noise ?
Have them Disconnect the amp and see if the noise still is there.
Or is the noise still there with the stereo off as the amp is on
anyway I think.
Or is it one of those 2011's that didn't get a Hi Fi system?
Do you have tweeters in the door sails?
The production date would indicate is has Hi Fi.
I will try and get a recording, the noise is electronic. Stupid question, can I start the car with the amp disconnected? Not sure if it will freak anything out. I can try that now.

The car does have tweeters in the sails, but is not the L7 system.
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      01-26-2013, 10:24 AM   #9
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Quote:
Originally Posted by ry335 View Post
I will try and get a recording, the noise is electronic. Stupid question, can I start the car with the amp disconnected? Not sure if it will freak anything out. I can try that now.

The car does have tweeters in the sails, but is not the L7 system.
Should be no problem. The "new" hifi amp (post 9/10) production does not reside on the CAN bus, whereas the old one did.
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      01-26-2013, 10:48 AM   #10
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Quote:
Originally Posted by taibanl
Quote:
Originally Posted by ry335 View Post
I will try and get a recording, the noise is electronic. Stupid question, can I start the car with the amp disconnected? Not sure if it will freak anything out. I can try that now.

The car does have tweeters in the sails, but is not the L7 system.
Should be no problem. The "new" hifi amp (post 9/10) production does not reside on the CAN bus, whereas the old one did.
Okay, I will give that a go. Last stupid question - is the amp connector have a plastic clip or does it just pull off?
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      01-26-2013, 01:54 PM   #11
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Quote:
Originally Posted by taibanl View Post
Should be no problem. The "new" hifi amp (post 9/10) production does not reside on the CAN bus, whereas the old one did.
No E9x HiFi amp ever used CAN wires.
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      01-26-2013, 01:56 PM   #12
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Quote:
Originally Posted by ry335 View Post
I assume it was not, they said they just replaced the "radio".
Considering that the OEM amp is the one that power the speakers and not the OEM HU, I would say that it should have been the first step in the troubleshooting...
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      01-26-2013, 07:21 PM   #13
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Okay, I'm screwed. I did a lot more testing tonight. Bad news, unplugged the amp, and the noise is STILL THERE! Ugh. At this point, I am sure it is safe to say it is not an issue with the radio or a noise coming from the speakers. Here is what I found tonight.

- Noise is very noticeable on startup. It is not there when turning over, but the second the engine ignition, the noise starts.
- Sitting in park, and fluctuation the throttle changes the level and pitch (not consistently) of the noise.
- Cruising at 50, and manually controlling gears makes it very easy to reproduce
- It is very easy to hear the noise when shifting into 5th gear from 4th.
- The noise is almost gone when in gears 1-4.

So... I am not sure what to make of this. I swear it sounds electronic, and I think it is voltage related. Which is why pressing the throttle changes the noise.

The good news, my iPhone picked up the noise. Please someone tell me you can hear it!

https://dl.dropbox.com/u/32292291/Memo.m4a
https://dl.dropbox.com/u/32292291/Memo2.m4a
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      01-26-2013, 08:27 PM   #14
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My ears aren't fresh you must have dog ears.

My ears aren't fresh and have been kind of abused but you must have dog ears.

Why don't you make a recording with the hood open in the Engine area.
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      01-26-2013, 08:28 PM   #15
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Quote:
Originally Posted by ctuna View Post
My ears aren't fresh and have been kind of abused but you must have dog ears.

Why don't you make a recording with the hood open in the Engine area.
It is very high in frequency, but you also need to play it back on something that can reproduce it. It is clear as day playing back on my iPhone, but I cannot hear it on my macbook.
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      01-28-2013, 06:01 PM   #16
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Quote:
Originally Posted by Technic View Post
No E9x HiFi amp ever used CAN wires.
Perhaps, I've never had one, but please comment on the attached (it specifically references changes between old and new HiFi amps, the newer lacking coding ability as opposed to the older).
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File Type: pdf SI B65 12 11 - HiFi Amplifier not recognized by ISTA.pdf (19.5 KB, 57 views)
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      01-28-2013, 06:23 PM   #17
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Maybe you could use your iphone as a meter.
See if it gets louder when the iphone is in different locations in
the car.

I thought equalization and signal levels for the Hi Fi amp were
taken care of in the Head Unit and there were only analog connections to the Hi Fi amp. If anything it looks like the newer one might be more likely to have data connections.

If the new Hi Fi amp had data connections and you put it into an older car without data connections in the harness of any type I could see how this would be the case.

This also might be why some of the people that retrofit to the new radio are having sound level problems with the old Hi Fi amp
and the New Head Unit retrofit. (its a speculation only )

Last edited by ctuna; 01-28-2013 at 07:12 PM.
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      01-28-2013, 06:40 PM   #18
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Quote:
Originally Posted by ctuna View Post
Maybe you could use your iphone as a meter.
See if it gets louder when the iphone is in different locations in
the car.

I thought equalization and signal levels for the Hi Fi amp were
taken car of in the Head Unit and there were only analog connections to the Hi Fi amp. If anything it looks like the newer one might be more likely to have data connections.

If the new Hi Fi amp had data connections and you put it into an older car without data connections in the harness of any type I could see how this would be the case.
Good thought, I did try that! Took the phone out of the car... I found a thread where someone said they had a very similar noise from a lose bolt on the cars transmission bracket. I'm going to check it this weekend.

I did take the car back to the dealer today, and they told me as they cannot hear it, my only option is to call BMW Customer Relations. Which sticks because I had three other people sit in the car that can hear it, so I am obviously not (that) crazy.
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      01-28-2013, 07:06 PM   #19
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Since you still have a lot of warranty

Since you still have a lot of warranty
You should be in a position to get a little leverage
some have gone to different dealerships and had better luck.
The fact that they changed the radio first does not tell me they
are very sharp.

Must be electrical if the iphone picks it up.
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      01-28-2013, 08:18 PM   #20
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Quote:
Originally Posted by taibanl View Post
Perhaps, I've never had one, but please comment on the attached (it specifically references changes between old and new HiFi amps, the newer lacking coding ability as opposed to the older).
That's interesting to tell you the truth, considering that BMW stated in the HiFi OEM amp description that:

Quote:
Stereo/HiFi amplifier
HiFi amplifiers are amplifiers with active frequency gates. Active frequency gates achieve better acoustic results than passive frequency gates.

The HiFi amplifier does not have speed-dependent volume adjustment or speed-dependent equalising. The function of the HiFi amplifier is only to amplify the low-frequency output.

The HiFi amplifier is a non-diagnosable control unit.
And there are no CAN wires shown in the schematics:
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File Type: pdf HiFi.pdf (135.0 KB, 27 views)
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      01-28-2013, 08:53 PM   #21
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Quote:
Originally Posted by Technic View Post
That's interesting to tell you the truth, considering that BMW stated in the HiFi OEM amp description that:



And there are no CAN wires shown in the schematics:
: just thought i'd share. I know people have complained before about the dealer "coding" their HifI amps.

I dont know ANYTHING about the canbus. is it possible serial commands are being sent via any of the other wiring?
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      01-28-2013, 09:44 PM   #22
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Quote:
Originally Posted by ry335 View Post
Okay, I'm screwed. I did a lot more testing tonight. Bad news, unplugged the amp, and the noise is STILL THERE! Ugh. At this point, I am sure it is safe to say it is not an issue with the radio or a noise coming from the speakers. Here is what I found tonight.

- Noise is very noticeable on startup. It is not there when turning over, but the second the engine ignition, the noise starts.
- Sitting in park, and fluctuation the throttle changes the level and pitch (not consistently) of the noise.
- Cruising at 50, and manually controlling gears makes it very easy to reproduce
- It is very easy to hear the noise when shifting into 5th gear from 4th.
- The noise is almost gone when in gears 1-4.

So... I am not sure what to make of this. I swear it sounds electronic, and I think it is voltage related. Which is why pressing the throttle changes the noise.

The good news, my iPhone picked up the noise. Please someone tell me you can hear it!

https://dl.dropbox.com/u/32292291/Memo.m4a
https://dl.dropbox.com/u/32292291/Memo2.m4a
Hey man, I can hear it! Check this out, I ran both files through a spectral analyzer. See that horizontal line at about 9-10khz? It begins a little after half-way in Memo and is there all the way through Memo2. Annoying! I also could not hear it on my Macbook, but heard it on the iPhone!
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