Driveline noise when decelerating down hill

G'day,

My '96 Cherokee, 95K miles, makes a humming noise when decelerating at high speed (take the foot of the throttle) or e.g. going down a hill on the highway. I can also feel a vibration.
Also, when I have to reverse up hill, the transmission seems to slip as I hear a grinding teeth noise from below. When driving forward at any speed there's no problem at all.
Somehow I think both problems are related but you guys might have an idea on this?

Thanks,
Guido

I 'think' that I found the problem! Some time ago the exhaust pipe was touching the cross member, the exhaust bracket was a bit sagged. We heated the bracket and we bended it back up. Apparently it's now too high and almost touching a bar at the top. When the engine gets driven by speed or so you're engine-braking, the torque causes the engine to move the in the opposite direction and so causes the bracket to touch the bar.........I'll bend it a little bit down again.:banghead: