FYI: For those do-it-yourself'ers out there. My 98 SLK230 began making a continuous thumping sound under acceleration. The harder I'd accelerate, the louder the sound. I jacked up the car and felt around for a bit and found that the "flex disk" that connects the drive shaft to the transmission has a chunk split off from it. As the shaft spins, the chunk spreads out and thumps against the floor panel.

Part was $40 shipping included. I'm going to do this one in my carport

Thought you'd all like to know.

 

Thanks. Ive visually checked mine, looks OK, no thump

Bazzle

 

UPDATE: Forget the carport idea! I had to borrow a friend's lift to get to it. Installation was pretty easy after that.