Yes - I have the same scary problem. Engine was rattling a bit for about 6 weeks - the best I figured from this website was an engine shock problem. Never fixed it but today the noise is decidely louder - and like a distinct knocking sound that i can hear inside the cabin. Scared that a rod about to go out or a valve coming undone?? Car sounds like a diesel or a Mack truck!
Engine Temp is 80-82, there seems to be some loss of power.
Checked the belt - which seems OK but I smell burning rubber? but then again I am neither an expert on smells (olfactory) nor on W202 engine.
I am looking for relevant codes to check/confirm the engine's health - and guidance/pictures on getting at the belt tensioner (?) problem - this is what the forum wisdom seems to suggest.
Till then - the C280 looks 'purty' just parked there.