Low humming sound from the rear
 

I new here and this is my first post. I have a low hum coming from the rear of my 2000 F-150. It sounds a lot like tire noise but it doesn't change with road, (pavement), conditions or surface types. I'm reasonably sure its a bearing but not sure if it is more likely in the differential or in a wheel bearing. As I write this it also occurs to me that perhaps a universal joint needs replacing. I had the pinion seals replaces 5 to 6 months ago. Does anyone have experience with this sound and its cause and/or cost of repairs?

If someone recently replaced your pinion seal, they may have overtightened the pinion nut and wiped out the pinion bearings.

I have a low hum coming from the back also. (1999) A mechanic told me the gears in the differential need changing. I'm assuming that's an expensive job. :(

Diff gears aren't cheap. Neither is the pinion issue. Keep the oils back there fresh.

Critical Setting:
 

:unsure:If the noise started after the pinion shaft seal was replaced, the tech that replaced the seal may not have properly set the pinion bearing preload. Unless the preload is correct the pinion gear is free to dance around and get out of critical alignment with the ring gear. The misalignment generally causes a whining noise, usually under acceleration, seldom under coast.

Resetting the preload may or may not completely eliminate the noise. Resetting the preload will draw the pinion shaft slightly forward as it takes up the wear of the rear bearing set. That slight forward displacement will upset the critical mesh of the pinion gear with the ring gear and the gear set may still be slightly noisy.....maybe yes, maybe no. :no:

If the preload is set to high, the pinion shaft bearings may wear rapidly and fail.:help: