I haven't noticed it doing it while at idle, but my car does have a rattling kind of noise when I acclerate very gently in first or second at very low speed. It sounds like it's coming from the tranny, but I can't tell for sure. It's done this since it was new, 25,000 miles ago, so I'm guessing that in my case, it's nothing to worry about. Just one of those mechanical noises cars make sometimes.
The dealer checked it out last year...they found nothing wrong. (but that means very little)
