I'm not sure if your situation lines up with the one I had a few months ago with a 126 gas car, but what Steve Brotherton just said fit my situation to a tee.
From a dead stand still, I'd accelerate and hear a grinding sort of sound. It was hard for me to tell exactly where it was coming from. Took it to a local independent MB repair shop and the owner noticed collapsed motor mounts. After he got it on the rack, he saw the tranny mount in about the same condition. You have 2 mounts up front for the engine and one for the tranny. Look at these before you buy something that may not solve your problem.