strange noise

[k-20]

ive had a strange noise in the truck for a while now,it seems to be coming from front of gear box?the noise isnt allways there,after driving for about 3/4-1 hour a bearing noise?? appears but when you push the clutch in the noise decreases to almost 0.a friend thinks it is the spigot bush,but i didnt want to pull gear box and transfer out just to lube the bush,only to find that its not the spigot!any sugestions would be greatly appreciated,thanks!