and the engine/transmission is under high load (accelerating hard). I had this happen to me once and it scared the crap out of me. Thought I hit a huge pothole or busted the driveshaft. I then remembered some of the messages that I had read on the board about this happening to others. I thought back a bit and noticed that last shift before the noise was a bit sloppy and the transmission wasn't fully in second gear. This may be the case with your car. Just be sure the shifter is completely in gear and run it. If it still happens, it may be a problem with your transmission.