[Itsprobablybroken]

09 E93 328i
Stock exhaust (Not PE there is no flap)

The noise is coming from behind the rear axle and is loudest/coming from right around the muffler. It sounds a lot like a heat shield rattle, sorta like a metallic wood pecker or a can of change.

This noise will only happen once the car is at idle, so a min or two after starting the car. If you rev the engine at all it stops and comes back once the revs get back to idle. I've tightened ever bolt and nut under the car and touched every heat shield and nothing will make it stop. I have taken off the stock exhaust tips too and this has no effect.

Here is the part that's making me the most confused. This noise ONLY happens when the AC is turned on. If I turn off the AC it goes away, but the sound is literally coming from the complete opposite end of the car.

Has anyone experienced this? Any help would be greatly appreciated. I've tried to Google it, but everything that comes up has to do with the stupid flap that my car doesn't have.

[travman33316]

I have the same exact issue on my 2010 E90 328i. I had the idle increased to make the issue go away, but I find that it makes starting with the manual transmission more difficult. Hard to start without the car shuttering. Still trying to figure out the rattle from the exhaust - only hear it at idle with A/C on.

[marvinstockman]

Could be the baffles inside the muffler.

[MoneyE9X]

I have a 335i and mine was the heat shield over the transmission.