What could be causing this high pitched whistle from engine bay?

[jmw_m3]

Just went for a drive and noticed a constant, high pitched whistle sound. It didn’t sound nearly as loud as it does on the dash cam footage - I could only barely hear it with all the windows up and low RPM.

I recently had both belts, alternator, AC compressor, & idler pulley replaced. Any ideas what this could be? Oil pump?

Dash cam video - E90 M3 engine whistle

[spammysammich]

Like this?
https://youtu.be/tCukQ3xfEWg

[Redd]

Originally Posted by spammysammich

Like this?
https://youtu.be/tCukQ3xfEWg

No, his sounds different. Like a constant whistle, not rpm related. Sounds like a persistent brake squeal. Does it go away when u brake?

[jmw_m3]

Originally Posted by Redd

No, his sounds different. Like a constant whistle, not rpm related. Sounds like a persistent brake squeal. Does it go away when u brake?

Yeah I don’t think it’s related to the plenum either since it still makes the sound at idle. Braking has no effect on the sound.

[jmw_m3]

Update: I didn't hear the whistle/whine for the first 45 minutes of my morning commute in heavy LA traffic. As soon as it opened up and I did a pull, I heard the sound while decelerating. The sound stayed consistent right until I pulled into my parking spot, when it just completely went away.

Does anyone have any ideas?

[spammysammich]

Smoke test it.

[Redd]

You know what it reminds me of? That feedback sound you get when the audio system isn't properly grounded. Did you make any audio changes recently?

Can the sound be heard from outside the car? Or only in the cabin. Try to disconnect the amp and see if it goes away.

[jmw_m3]

Originally Posted by Redd

You know what it reminds me of? That feedback sound you get when the audio system isn't properly grounded. Did you make any audio changes recently?

Can the sound be heard from outside the car? Or only in the cabin. Try to disconnect the amp and see if it goes away.

Yeah it does sound a lot like that! I had the same thought, but I haven’t touched the audio system and it can be heard from outside the car when in my garage.

I just took the below video and it’s definitely coming from under the hood. Kind of seems like the passenger side, but it’s so hard to tell.

engine bay whistle

[spammysammich]

Originally Posted by Redd

You know what it reminds me of? That feedback sound you get when the audio system isn't properly grounded. Did you make any audio changes recently?

Can the sound be heard from outside the car? Or only in the cabin. Try to disconnect the amp and see if it goes away.

I missed the point that it seems rpm independent. My hearing is pretty shot on the high end from shooting without earpro when I was young. I turned up the volume until I could properly hear the example and it does seem more like an electrical issue. One of my cars makes a loud constant high pitch whine when I have my bluetooth adapter turned on but no signal from it to my aux port. If i unplug my aux connection it goes away. I can't hear it outside the car.

Could it be that OPs noise coincides with when the alternator is charging?

[Redd]

Originally Posted by jmw_m3

I just took the below video and it’s definitely coming from under the hood. Kind of seems like the passenger side, but it’s so hard to tell.

engine bay whistle

Definitely not audio/electrical. Definitely mechanical, coming from passenger side of engine bay. Sounds like bearing whine. Check your belts, and pulleys.