I have a 98 CLK320. Starting a few months ago, I've noticed a light thumping noise coming from the engine bay on cold mornings. It's most noticeable when I'm stopped at a light, and the engine is at idle speed. It's not very loud, but it happens at regular intervals (one "tap" every 1-2 seconds). The car didn't do this at all when I first got it, even during the coldest starts. I change the oil every 3000 miles with Mobil 1 10W30, and keep all my fluids healthy. Any idea what this might be? I haven't taken it to the dealer yet, largely because they seem to have difficulty solving ANY of my problems, and the service is horrid. Thanks for any help you guys can offer.

On a side note, there are all sorts of creaks and rattles, but I've heard this is a common problem with CLKs, especially MY98-99. Again, the dealer is of little help. Any suggestions?

-Daesun