Hi. Could some one help me or give insights on what the problem (and repair cost) would be?

I drive a 2000 Lynx Ghia (and a 1996 Mazda 323 GLXi A/T). As I was backing up the Lynx this afternoon, an ugly grinding noise coming from somewhere in the transmission area suddenly came about and the vehicle would not move. (The noise was like shifting gears on a manual transmission without stepping on the clutch, but milder.) The grinding noise would be present in all positions except Park. However, when shifting from Reverse to Park, the grinding noise would be present but would go away in around 1 second. In the Drive positions, in addition to the grinding noise, the speedometer would register about 20kph even if the car is not moving.

I checked the ATF level and it is OK.