Toyota Repair: Im stumped! Help.

Question
I have A 89 Toyota pickup 4x4 manual transmission  22re.  This started last year when it was cold outside.  When I'm going down the road it makes a roaring noise.  Cant pinpoint where it's coming from. But I think it may be towards the rear of the truck. it used to do it for just a few miles then quit On and off. If I hit a bump it would quit.  When the weather warmed it quit completely but now it's getting cold again.  It started out the same on and off and would quit, then it got more frequent for longer periods  but today when I was driving home from work it was constant and very loud.  It only does it when cold.  help!  Any ideas

Answer
Hello, while the noise is there take the truck out of gear and let it coast, if the noise stays the same the problem is most likely a rear ale bearing, if the noise goes away it's probably a transmission bearing or differential bearing, if the noise goes away in only fourth gear the problem is the transmission, if the noise never goes away no matter what it's in the final drive(differential).