Diagnosing Odd Engine Noise

[C Dome]

Hey everyone, early this week I noticed an odd “metal” sounding noise from the engine bay today while driving. I only noticed it at complete idle (600rpm roughly). Anytime I go near the throttle it instantly goes away, even just a hair of throttle and it’s gone. For example, with the A/C completely off, you can hear it at idle. When turning the compressor on and the revs pick up slightly, it goes away.

Hard to tell exactly where the noise is originating from. My initial thought was one of the pulleys. I didnt notice any obvious signs of vacuum leaks but I could be wrong.

Has anyone experienced something similar or have an educated guess? When I have time I’ll remove the intake plenum and see if I can better pin point the noise.

Car is a 2008 E90 M3. Recent maintenance in the last 2k miles has been oil filter housing gasket, belts, water pump/thermostat, fuel breather valve, etc.

Attached video is the loudest I’ve heard it. Normally, it’s very quiet inside and outside the car. And it hasn’t gotten this loud again yet, it’s been a few days.

Thanks for the help!
-Chris


*Edit* Trying to post the vimeo link from my computer instead, it doesn't seem to be uploading by phone.
http://vimeo.com/875330803

[Theodore]

Sounds like a pulley is failing and the most common pulley to fail for this engine is the idler pulley. Check out this DIY thread here.

[C Dome]

Originally Posted by Theodore

Sounds like a pulley is failing and the most common pulley to fail for this engine is the idler pulley. Check out this DIY thread here.

I appreciate the reply, this is what I was leaning towards. I'll look into changing it out soon then.