well you need to jack the car and grab all the links and make sure none are loose. Look at the inner and outer control arm bushings. Also drive the car and pull a little on the parking brake...those can come out of adjustment and rattle quite a bit. The 300e had an upgrade on the parking brake pads tp stop the noise. Check the subframe mounts also. Twist your driveshaft and make sure its not the dreaded flex couplings which suck on mercedes. Sometimes noises are referred sounds. Most of those things you can fix yourself with the exception of the outer control arm bushing which is a pain. But it does clunk when bad.