Car: E46 M3 (2003)
Miles: 37K

While rolling up to a stop light yesterday I noticed a loud noise from under the car which sounded like a bunch of marbles in a car bouncing around. I just finished shifting from 4th to 3rd and then into second and when I disengaged the clutch and rolled to a stop the noise started. I figured I picked up a rock or something and it was in the rim. The sound went away and I didn’t think much of it. I then heard it again the same day under the same conditions and then again when I was parking my car at work today.

I am starting to think there is a problem either with the clutch or transmission.

I just had the transmission fluid flushed on 06/06/11 by a very reputable shop.

Any ideas?

Thanks!