Noise from rear diff

[modular]

This is on a 1997/standard cab/shortbed/ 2WD 7.5 open rear end. At around 30 mph I start hearing an oscillating humming noise from the rear diff (humm-quite-humm-quite-humm). It is slow like it has something to do with the ring and pinion and does increase/decrease with my speed under acceleration and coasting and both in and out of gear. I put it up on jack stands, put it in 3rd gear and can duplicate the noise with no weight on the axle. It is coming from the diff and the noise resonates up through the bed. When I had my alignment done they did find a bunch of plastic wrapped around the u-joint at the rear diff. No leaks are present and it is stone quite until 30 mph and dissapears at about 55 mph. Is this the pinion bearing making noise? The truck has 81K on it. Thanks for any insight.

 

[Explorin94]

The plastic wrapped around the driveshaft/u-joint threw the driveshaft out of balance. That in return my have taken out a pinion bearing. The bearings are no big deal to do especially the very first one. Just take the flange off and pull the bearing out after the seal is pulled out. Try replacing just that bearing to see if your noise goes away. Mkae sure you do a seal with it. If the noise is still there then you need to drop the whole gear assembly out the rear cover and replace the other pinion bearing. If you go that far might as well replace all the bearings and seals too.

 

[MAKG]

The FIRST thing to check with funny noises is ALWAYS the brakes.

Especially if you have rear disks. Disks do not need the pedal depressed to make (light) contact.

This doesn't sound like a pinion bearing to me. Those are almost 4 times faster than the wheel, so at 30 MPH, those go by FAST. It would be a constant whine. It's around two feet per bearing rotation, at a speed of over 50 feet per second.