I'm driving an '07 convertible S. Right after I put on new run flat tires I began to hear an intermittent, non-rhythmic clunk/clump between the 30-40 mph. I sounds like a gnome with a plastic boots is giving a kick under the center of the engine compartment. The only thing predictable about it is the speed at which it occurs. It's not a metallic sound, or squeaky or rubbing. Knock on an empty plastic container to get an idea.

The dealer had it for two days and couldn't find anything. The tires have been checked. Has anyone had this problem? Does anyone have any suggestions of what it might be?

Appreciate your help.

 

Id start by checking the lugs, then making sure that any new wheel weights arent hitting brake calipers or anything like that.

Wonder if anything fell inside the tire?