4x4 sticking partialy in gear?

[jeremiahweed28]

I picked up an 88' Silverado 2500 not to long ago.
Every time I Take it out of four wheel drive, I hear a heavy metal grinding while the truck is in motion and the noise slows and stops as the truck slows and stopes, but starts againg once the truck is moving. The 4x4 light stays on for a bit also, and as soon as the light goes off, the grinding stops. I am using the 4x4 as little as posible for fear of making things worse. I cant tell if the grinding is coming from the front drive shaft or the transfer case or what, but its definatly under the front of the truck. I think it may be sticking partaly locked in 4x4 but I have no clue how to fix that or where to start looking for the noise because I can only hear it while i'm driving.

Has anybody ever had this problem or does anybody have any Idea of how to fix it?
Any help or input is greatly apreaciated.

Thanks,
-JW