I got 6ok miles out of my head because I believed I saw it in the owners manual (2000, Florida heat). Sunhunter, that grinding you hear are your syncros not syncing the engine/tranny speed. I've noticed the Insight doesn't have very good syncros and mine have been gringing the gears since <20k miles. I find the only solution is to upshift slowly and deliberately. To downshift, always double clutch (even with syncros) because the whole weight of the car is on those syncros. I've got the extended warrenty so I'm probably going to bring it up with Honda sometime before that warrenty ends to see if they might do something with it (I''ve seen other manufactures replacing the transmission). Anyway, there's no harm in replacing the MTF early; hope it helps.