After living with some really annoying squeaking and rattling from the driver's door + the seal between top of driver's side window and rubber seal, I took the car in for service and put in a service request.

Turned out a worn window regulator was the culprit. It was worn out. Not to mention it wasn't making good seal anymore.

A day later and $0 (well.. some money for the c280 loaner's gas and my car's gas to drive it to the dealer and back)... the squeaking is reduced to almost nothing (totally bearable)

The passenger side's window is squeakier now.

But of course, there's still those weird squeaks from the back seat area, and where the cable for the orthopedic seat control hits the seat frame (which I thought I had fixed by padding it)...

What to do I guess, it's a pretty stiff car...

Thought I'd give a heads up in case anyone else has the same issue. Check the window regulator.

By the way, this is a CLK55 with 28000 miles on it.