On my 98, 4wd, 1/2 ton, I have a low pitch, oscilating, hum coming from the
rear that is especially noticeable when I hit 65-72.
I had a similar problem and vibration before that and had one of the
u-joints replaced which fixed the vibration, but there is still an annoying
hum, with maybe a slight vibration. I have also had the following done since
1) New axel bearings
2) New carrier bearings
3) New tires
4) New ball joints
The mechanic wants to have the balance of the drive shaft checked next. He
said he sends it to a place that spins them.
I'm just afraid that I'm getting into a time comsuming, expensive
troubleshooting process at this point, and could use any advice or
confirmation of the approach.
I took it on the highway and put it into neutral while it was making the
sound and the sound didn't go away. I don't know if that eliminates
anything. In my mind, it does eliminate the exhaust as it almost sounded
like it could be causing the problem.