This has happened twice now and was wondering if my gearbox is on its way out or what. Basically had a play with a Mk4 Golf GTI Anni and yes I won

, anyhow as I legged in first and put in second I felt a Jolt

. I know the second on the gti is weak and crunches but it was a just a jolt as if heading it with a hammer ?!?!?! The car is not mapped and I have a uprated Dogbone gearbox mount so not sure whats going on??
Is this normal or something I am doing wrong. It might be that I left the clutch too early
Any Ideas??