Help! Growling sound coming from rear only with AC on

ColdUpHere · 10-07-2021, 11:41 AM

Hello friends! I have racking my brain with how I can get rid of this growling sound I am hearing coming from the rear of the car while inside the cabin! Before anything, here is a video showing the sound...You can hear the sound at 0:15 in the video:

Link to video

So far, I have noticed these things:

This sound can be replicated at idle only with the AC on (not just the blower, I must hit the AC button for the sound to appear)
The sound seems to be coming from the rear passenger side floor or potentially under the passenger side front seat
I am able to feel the rear passenger side floor vibrate in accordance with the sound
This sound can sometimes be heard when I am cruising at highway speeds (even with the AC off)

Any ideas are helpful as I have NO idea what this could be and am on the verge of deafness from cranking the stereo up to cancel out the noise.

haaken675 · 10-07-2021, 03:11 PM

The a/c puts extra load on the motor and can cause more vibrations. As an example, my car has solid motor and trans mounts. With the a/c off the nvh isn't terrible. With the a/c on it's much more noticeable at idle.

It is possible that you have worn out bushings allowing for more movement. At a minimum i would check heat shields and splash guards to makes sure they aren't loose and vibrating. If this only happens when moving, likely center support bearing.

ColdUpHere · 10-08-2021, 08:12 AM

Quote:

Originally Posted by haaken675

The a/c puts extra load on the motor and can cause more vibrations. As an example, my car has solid motor and trans mounts. With the a/c off the nvh isn't terrible. With the a/c on it's much more noticeable at idle.

It is possible that you have worn out bushings allowing for more movement. At a minimum i would check heat shields and splash guards to makes sure they aren't loose and vibrating. If this only happens when moving, likely center support bearing.

That would make a lot of sense. When the AC compressor kicks on, I am able to feel a lot more vibrations as a whole throughout the cabin.

Time for me to start replacing bushings and mounts haha

10-07-2021, 11:41 AM	#1
ColdUpHere New Member 3 Rep 11 Posts Drives: BMW 335xi Join Date: Oct 2019 Location: Ontario, Canada iTrader: (0)	Help! Growling sound coming from rear only with AC on Hello friends! I have racking my brain with how I can get rid of this growling sound I am hearing coming from the rear of the car while inside the cabin! Before anything, here is a video showing the sound...You can hear the sound at 0:15 in the video: Link to video So far, I have noticed these things: This sound can be replicated at idle only with the AC on (not just the blower, I must hit the AC button for the sound to appear) The sound seems to be coming from the rear passenger side floor or potentially under the passenger side front seat I am able to feel the rear passenger side floor vibrate in accordance with the sound This sound can sometimes be heard when I am cruising at highway speeds (even with the AC off) Any ideas are helpful as I have NO idea what this could be and am on the verge of deafness from cranking the stereo up to cancel out the noise. Last edited by ColdUpHere; 10-07-2021 at 11:43 AM.. Reason: Adding additional clarification
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10-07-2021, 03:11 PM	#2
haaken675 First Lieutenant 101 Rep 304 Posts Drives: 24v turbo e30, e92 335i Join Date: Feb 2020 Location: FL iTrader: (0)	The a/c puts extra load on the motor and can cause more vibrations. As an example, my car has solid motor and trans mounts. With the a/c off the nvh isn't terrible. With the a/c on it's much more noticeable at idle. It is possible that you have worn out bushings allowing for more movement. At a minimum i would check heat shields and splash guards to makes sure they aren't loose and vibrating. If this only happens when moving, likely center support bearing.
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