I was thinking maybe it was the freewheel tightening too... but why only from the stops? I was climbing a good size hill with my son not pedaling and my daughter in a trailer on the back and I didn't feel anything. But I pulled away from a stop sign last night and felt the same thing. All the other stops on the ride felt fine. It's been maybe 4 or 5 times that I've felt it.. after 4 or 5 revolutions on the pedal it seems to stop.