My 2001 A8L has a low pitch rattle coming from somewhere around the driver's side wheelwell. I can feel the rattle in my left foot as I am driving. It is most pronounced at low speeds. It gets worse the longer I drive the car. It has the sound of a loose part but three different mechanics have assured me that everything is secure. They are stumped and so am I. I have had the tie rods changed, new brake pads on the front but no change.
Any ideas?

 

could be the heat shield on the exhaust or something like that

 

I had a similar rattle this past summer on my previous car, an 02' 3.5 Altima. Turned out to be a front wheel bearing.

 

a hum that gets louder on speed = a bearing, a vibration from the underside of the car "if quattro/4 wheel drive" means prop shaft UJ joints or doe nut rubbers/bearings or seals