RX300 All Wheel Drive problem

[97blackhawk]

My 2000 RX300 is having some sort of gear (?) problem. Was at the tax office for vehicle registration. The parking lot has been repaved a half dozen times, leaving a nice dip at the end of the parking space where the layers of blacktop drop off to the original pavement bordering the curb. I had set my front wheels right into that dip.

When I tried to leave, I put it in reverse, hit the gas, and it rolled back to the layers of blacktop and stayed there. I revved, and it didn't seem to even try to jump over it. I doublechecked that I was in reverse and not nuetral, and revved again. This time, at the highpoint of rpm's, and with a sudden jolt, the car flew over the ridge and out of the parking space. After that, for a few miles, it would respond with grinding when I would take off from a stop, and then go away. Since then, every now and then, the grinding momentarily returns, usually when changing to reverse and first taking off. The noise may not return the rest of the day.

My amateur theory is that the full time 50/50 power had a hard time jumping over that ridge, and the car finally threw more power to the front. The transfer was very sudden, and may have screwed something up. I also can't seem to reliably reproduce the problem.

Any ideas on what might be broken?