02' Ranger XLT 3.73 A Rear End Help - Diagnose Humming Noise

[sheliable]

My truck makes a humming/whirring noise that seems to reverberate up through the bed and cab as I accelerate and am maintaining 25-50 mph speeds. Even at highway speeds, you can still hear it.

I have thought that most likely it is the rear differential with a bad pinion bearing or something causing the noise. (I don't know exactly what that bearing does, but I do know what the diff's role is, and that the bearing is tough and expensive to replace). It is not a limited slip. I'll post the tag code when I can remember where I put the thing/pull it from an old post.

I have looked at the rear diff twice now. There are no chipped or ground gear teeth. In my opinion the diff looks like it's in really good shape. The first time I looked at it almost a year ago, the fluid was milky gray and looked pretty bad/old. I obviously, changed it sealed it back up, and this time I looked maybe 10k or more miles later it looked pretty good/fresh still. Here's a picture I took of it last night, I'm not sure if the spacing where the arrow is is normal or not, but that's the only thing that looks possibly off to me.

I am thinking I need to remove the driveshaft, rotate it and watch the diff cycle through maybe. Then I was thinking I should probably replace the U-Joints and see if the humming noise persists. I'm asking for your guys help to identify the proper U Joints to buy from Rock Auto or AutoZone to replace them with. Additionally, any recommendations for things I may as well replace while I'm doing the U-Joints to possibly solve the noise? Is there anything other than the rear differential to check for making the noise? I don't think it's the transmission? I dont really ever have issues shifting gears or anything.

Do you think my only other option if none of that works is to junkyard swap a whole rear axle assembly?

'Thanks in advance for your help.

 

[RonD]

Arrow is pointed at the end of the axle shaft, yes there will be a space, thats the in/out movement you feel when tire is off and you pull and push on the axle

Have the tires been rotated front to back, yet?
You should do that, see what hum does

When going downhill shift trans to Neutral, see what hum does, does it change with speed or engine RPMs

I assume applying brakes doesn't change the noise?

Find an open road and do Reverse for a distance to see if hum is present


Yes, whole axle swap is best, 1993-2009 Ranger or B-series will be plug and play
You could even put in a limited slip


Rebuilding a differential is just wrench work up to a point, then you need to shim the pinion for the ring gear, and shim the spider gears for differential mount
In theory if you keep track of the current shims placement and don't replace anything but bearings and seals then it should be good to go, but thats only "in theory", real world applications often "poop on" theories, lol