Hello,
I just picked up a 97 Grand Cherokee Limited with a 4.0 and quadratrac.
The truck makes a grinding noise that seems to come from the axels and or the transfer case, hard to tell exactly where. The noise level goes up with the speed. At 60 it gets louder and then at 70mph the truck starts vibrating that feels its coming from everywhere. After I pass 75mph it all quiets down and the truck runs smooth. At 80mph the vibration is completely gone but i can still hear a little grinding.
Trans shifts fine, engine sounds good. Its my first Jeep so I'm not familiar with the normal sounds it makes but this seems too loud for normal.
Where can I start the trouble shooting to find the problem? Any help is very appreciated.
Thanks

 

Have you checked all your fluids, Transfer case and axles,

 

I had the same problem on my 99 all stock suspension, ended up being a bad u-joint and abd wheel bearing in the front axle.