I would have that same problem when putting into reverse right when i'd start it up. i put another quart of fluid in there and it stopped. I also get a buzz when it shifts sometimes, and also some-what a whining noise when the rpms climb (when boosting) I know i used to, but i dont know now since when i do drive it, it's usually with the dump open and i havent really listened to it recently.
Havent had any problems with the trans, ive raced it, have around 10k on it probably, and no problems with WOT L/U or anything, and the fluid is always perfect!
-Adam