I have a '97 540i. I have a loud rumbling type noise that is coming from under the car...sounds like its coming from under the center console area, but under the car. Problem is worse while driving in heavy rain or slushy snow. When noise is present, I can make it worse by travelling over small bumps. Almost sounds like something banging against the underbody of the car, but in the center od the car...not a front end noise.

Also feels like the car is working harder to accelerate.

Any thoughts on this would be greatly appreciated. Dealer is clueless on this, and I am positive there is a problem here...and I have checked the archives and have found that others have heard this on their car but there is no solutions listed.