I'm having the same issue but I'm under warranty aaaand will be seeing the dealer next week..I guess I'll keep you guys posted

 

I also have a 2008 528i with the same type of issue. At idle the whole interior resonates with a low frequency booming sound. There is a write up on this problem here: http://www.bimmerfest.com/forums/sho...d.php?t=378630
The problem appears to be due to clamps used to attach the exhaust to the car body and is described in a technical bulletin from BMW.

Before seeing this bulletin, I had taken the car in for service twice for "rough idle". Both times the techs at the dealer tried a few things (or at least they said they did) but the problem was not resolved. I gave up thinking this is yet another one of those "BMW Engineering" things (like the noisey steering pump, pulleys, excessive tire noise, steering pull to the left etc. etc.

I am talking to the dealer again - armed this time with the Bulletin mentioned in the above link. But now my original 4yr warranty has expired and the extended warranty does not cover exhaust related issues. I will see what my dealer says - the service rep was going to check if they can do something under "goodwill". I will update this post when I get their final response.

 

I have a stable RPM 545i. I do hear a humm sound, mine sounds like metal clicking. Its present when the car is cold, even when im driving at low speeds/rpm i hear metal clicking. Usually when it's warm the clicking goes away but the Hum still says.