Rear Diff Replacement at 36k

i did it for 100k miles on two different third gen tacomas. Stayed on top of maintenance and never had issues, so my vote is no.

 

Did they do any other diagnosis besides just draining the fluid and you saying it whines? As stated they all whine to some degree and a bit of metal in the fluid is normal so without hearing it or playing with it hard to say if anything is wrong. From the little information we have I would guess it's fine.

If you can jack up one rear tire and put the truck in neutral you can turn the driveshaft and see if it feels crunchy, extra stuff or has excessive play. Did they indicate any such indication from when they had it on the lift?

 

This might help give you some idea what things should look like: https://youtu.be/JNFjcx8m7Hk?si=G9OuoS6A-yY_9ca-

 

You could replace the whole axle for 3.5k.

 

Checking the torque on the pinion nut would be my first move. I've seen it...