S4Killa

I was sitting in bumper to bumper traffic for 45 minutes today. It was literaly stop and go. After awhile I noticed a thunk sound and felt it from the transmission. Then a few minutes later I was idling(no pressure on gas pedal) while moving at ~5mph and when I put pressure on the gas pedal to speed up some, the same thunk sound, as if tranny slipped then caught. Car only has 1300 miles. Was I just lucky and hit the spot where the tranny is auto shifting and when I pressed on gas pedal it wasn't ready?? Just curious. Maybe April can help with this one. Sorry I can't explain it any better