I have a 1990 Toyota 4runner 3.0l with an auto tranny 4wd. There is a whirring noise coming from the back end of the 4runner when the windows are up(if windows are down or radio is on you can not hear it, windows must be up). It sounds different at all speeds and doesn’t change when slowing down or accelerating(as in the noise doesn’t go away). Also when going down a hill if I put the truck in neutral you can still hear it. I think it could be the pinion bearing or maybe a wheel bearing. It is most noticeable at about 40mph and after about 65 it is a lot harder to hear the noise and you cant hear it under about 20mph. Any help would be greatly appreciated. I just had the tires balanced and rotated and that didn’t change anything. Thanks

I read about wheel bearings and that might be it to It said to turn the vehicle so it sways and if the noise goes away when you sway or turn a certain way it might be that. I just went and did that and it seemed to go away when I turned right so the vehicle swayed to the right. I am gonna go drive it again and try that a few more times.

 

Jack up the rear of the truck so both wheels are off the ground..
spin the tires, dont worry the opposite one will spin..
if you hear anything, take note of where its coming from.
Play with the pinion flange.
Grab it and see if theres any play. If the pinion flange moves in any way, then the pinion bearing is gone, and it's time for a rebuild.

 

I did the wheel one and on the left side i can hear a scraping noise. Nothing from the right side though and also after driving more when the car leans right the noise goes away but when the car leans left it dosent. How do I check the pinion flange? Any body have a picture of what It is? Thanks

 

Left side wheel bearing maybe.

 

So, resetting the preload won't help, eh? I'm asking because I'm in the same situation with my rear differential. If it does mean "definitely" need to rebuild, how long could I get away with it as is? IOW's, I know there's variables involved, but will the entire pinion/ring go toast riding around like this for a little while? I don't go offroading or anything. Just some country road driving and inner city/highway stuff.