I've had a whining sound coming from under the driver side of my truck for a while now. The noise increases with speed, and is the loudest around 40mph. I haven't used 4wd in a while, so I thought it might be the l/f wheel bearing. The other day I clicked into 4-high on a dry paved road and the whining sound got a lot louder. When I put it back into 2wd it went away again. I changed the fluid in it last night but the noise is still there. The truck has 53k on it, and I don't think the t-case fluid has ever been changed before yesterday, it was pretty brown when I drained it. Any ideas?

 

yeah mine does the same when in 4 wheel, i think a little whine is normal.