Anyone know how to diagnose a whine that might be a bad pinion bearing?

I only hear the whine when slowing down but I can’t tell if it’s the front or rear.

With the oil seep from my front diff, I’m suspecting that first. Although if I’m not using 4wd, would that mean it has to be the rear?

Also, can I wait till spring to deal with it if that’s the issue?

 

Front diff still spins even when not engaged.

jack it up, and give the pinions a wiggle. Maybe listen for crunchy bearing while giving it a spin. I've got a stethoscope, but i've heard you can listen through a ratchet extention or screwdriver.

open the diff fill plug and try to dip something in to see how sparkly the fluid is.

 

piece of broom handle works good too

 

Good advice. Thanks.