I also purchased a 2008 528i a month ago with 19,000 miles and it idles very loud. Some days are worse then others. The car runs great and as soon as I touch the gas the noise/vibration sound stops.
It is annoying and I cant get used to it.
I took it back to the dealer and a mechanic sat in the car with me for 15 minutes and told me there is nothing to be done. He said it is the number 1 complaint with 5 series BMWs. It has something to do with the vehicle trying to use minimal gas at idle. The vehicle barely runs at stop to burn minimal gas and as a result a bass like vibratory noise occurs. The seats or steering wheel do not vibrate, it sound like there is a small bass tube in engine. If they could just slightly raise the idle it would be quiet like my lexus. I was told nothing can be done.
If anyone has any ideas let us know..
At times I find myself pushing on the gas which increases the idle a minimal amount which stops the humming noise.
Last edited by damonwhite; 10-14-2009 at 07:00 PM.