Im guessing they mean the one way bearing that makes the second gear work... i wouldn't of thought it would be that because it would be more when moving from a stand still... its the same kinda bearing as in the pull start and when they stick you might know your pulling it and it will catch now and then.

I have seen it happen on a mates car where he used it in a very dusty place mostly which wore the bearing badly enough that when he gave it throttle the engine would scream while the car was hardly moving, then the bearing would grab, unleashing all that stored energy from the engine launching the car like it had a rocket in its exhaust..... fun to watch but the diffs/drive shafts wernt vary happy

anyway this don't sound like its the one way bearing to me... how fast would you say the car is going when all this happens? has it always been this way or did it just start happening?