Suburban hum

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 then:
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.
Thanks, Fred
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Swerve slightly from 1 side to the other. Does the noise change in one direction? If so most likely an axle brg. Larry

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That might help.

It could also be an angularity problem in the drive shaft itself. When u-joints flex, they don't do so in a linear fashion (CV joints don't have this problem), so if there is too much "bend" at a u-joint, the hum will come from the varying rates (velocities) that the joint(s) bend and unbend. Angularity hum doesn't usually show up intil 45-55 mph, at least it didn't on my truck (made some wedges to rotate the rear axle slightly, which took care of it). Angularity hum will cause premature u-joint failure.
HTH, Pete
--


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.