[TDF9]

My 2006 325i 6MT makes a low droning noise that rises and falls with engine speed, and completely disappears when I turn off the HVAC system (by lowering the fan speed to zero, so the whole system goes off).

The HVAC fan also occasionally squeaks, so it's on my list to get to it under the dash and lubricate it. But I'm inclined to think this whining / droning noise is an entirely separate issue, as it's not a function of fan speed but, again, engine speed.

It's subtle but quite noticeable and irritating. Each time I pull away from a traffic light I hear the droning noise rise in pitch as the revs rise.

If the noise were coming out of the stereo system I'd think it was some form of electrical interference from the engine ignition system, or inadequate shielding. But alas, no connection to the stereo system being on - noise persists so long as HVAC is on (and regardless of what speed the fan is set to).

Anyone ever experience this? I appreciate any ideas!

[lab_rat]

Originally Posted by TDF9

My 2006 325i 6MT makes a low droning noise that rises and falls with engine speed, and completely disappears when I turn off the HVAC system (by lowering the fan speed to zero, so the whole system goes off).

The HVAC fan also occasionally squeaks, so it's on my list to get to it under the dash and lubricate it. But I'm inclined to think this whining / droning noise is an entirely separate issue, as it's not a function of fan speed but, again, engine speed.

It's subtle but quite noticeable and irritating. Each time I pull away from a traffic light I hear the droning noise rise in pitch as the revs rise.

If the noise were coming out of the stereo system I'd think it was some form of electrical interference from the engine ignition system, or inadequate shielding. But alas, no connection to the stereo system being on - noise persists so long as HVAC is on (and regardless of what speed the fan is set to).

Anyone ever experience this? I appreciate any ideas!

Sounds as though it could be one of two things: 1)the HVAC blower motor is going out or 2)the bearings in the pulley of the A/C compressor are bad.

You may know this already, but in case you were not aware, there is a safety recall on the wiring in conjunction with the blower motor. See this link for recall details:
https://static.nhtsa.gov/odi/rcl/201...7V676-3259.pdf

Part number (blower motor):
https://www.fcpeuro.com/products/bmw...cm-64119227670
[FCPeuro has lifetime parts replacement, which is the best in the market]


See this link for blower motor replacement instructions:
https://www.pelicanparts.com/BMW/tec..._Replacing.htm

For the second issue:
There is a thread from a Canadian guy who replaced the pulley/bearings in the A/C compressor as opposed to replacing the entire unit; IIRC he had good results.

I will do a search and post a link here if I locate it.

[smass]

Does the noise go away when you hit the snow flake button? If so that is the AC compressor which is a common noise on our older cars. Mine has been making this noise for 5 years now.

[ewicky]

There's also the fan inside the HVAC control area for positive flow on the interior temp sensor. Mine was making noise. Blasted it with compressed air, and it's all good now.

I've noticed plenty of things faux-in-time with engine speed. That is to say, that when the engine revs, so does the fan. But that's only because the voltage goes up as the alternator spins above idle. We don't normally notice the voltage drop at idle because our smart cars regulate the voltage to all the lights separately. (It's incredibly evident with a Hazard Fraught tire pump. That thing revs up and down with minor changes, because the cig sockets are not regulated)

[TDF9]

Thanks, all, for these ideas.

Will turn off the A/C next time I drive it and see if that makes a difference.

Can you offer more on where this is or how I find it: "also the fan inside the HVAC control area for positive flow on the interior temp sensor"?

I didn't know about the recall, so certainly will follow up on that!

[N52bigblock]

Yes definitely check if the noise goes away when the A/C is turned off. I had a similar noise in my car. For some reason the A/C compressors on these cars become noisy if the system is low on A/C gas. I serviced my system with our A/C machine at work and the noise is now completely gone. It only had 220 grams of gas left in it. It is supposed to have 600 grams. It is recommended to have your A/C system serviced every few years, but hardly anybody does. If you haven't had yours done for a while, this could possibly be the issue

[TDF9]

flipping off the A/C ended the noise right away. Can't believe I didn't think to try that. Thank you! So I am very interested in the AC compressor pulley bearing DIY - will go search for that now...