Pathfinder Tranny noise

My '99 Pathfinder has started making a noise while in park and neutral at
idle, but not in drive or reverse until accelerating. The noise is
something of a loud whine, and is present when the engine is first started.
Using a scope, it seems the sound is most pronounced at the output of the
transmission where the driveshaft attaches. At one instance, my wife could
not make the vehicle go either forward or reverse. She killed the engine
and sat for a minute, restarted, and was able to move. Any ideas as to
what this could be?

Thanks,

Don J.