Ha ha, I don't miss that sound. It's even worse when the CLACK is accompanied by a trapped finger or bit of skin!
I guess the only thing you could try is a couple of lines of sticky back padding of some sort. As long as the lever is able to return home then it'll be fine. It's been a while since I had one so I can't remember exactly how they look on the under-side.
Few lads on here have them, they may chirp up soon enough