My SL500 has an annoying "rotational" noise at idle. This noise goes away the instant the revs rise and is never present when driving the car, but each time the engine returns to idle spped the noise is present and especially audible when in a confined space such as a parking garage. It almost sounds like a misaligned belt or a tensioner bearing beginning to fail. The dealer service department examined it and proclaimed it normal valvetrain noise for the 113 engine. They went as far as to remove the serpentine belt to see if the noise went away but told me it didn't. The noise isn't that bad and would not be a consideration in a lesser car, but doesn't seem appropriate for an upper-end vehicle. Has anyone else experienced this? I've had Porsche's and Corvettes which were noisy, but it was a more pleasant mechanical noise. The noise coming from my engine is not pleasant at all.
Red Line Oil-"Slicker than snot and twice as tasty"
on my 2003 SL 500 (59,000 miles) I hear an occasional noise (as you described) while in garage right after starting (with cold engine) --then goes away in less than a minute. (I assumed it was belt noise--'have never taken in for service for that issue.)