Bad hub?

[exbass94]

94 Explorer in sig...has factory auto hubs. I've been using 4wd fairly often lately with all the snow we've been getting. It's been working fine as far as I can tell until this morning. I was backing out of my driveway and I hear a deep "thunk...thunk...thunk...." every second or so. It seems to come from the passenger side. This is different from the ratcheting noise they usually make when they go bad. It only happens in reverse (happened again when I got to work and backed into the parking space). 4wd wasn't used the last time it was driven, so the hubs should've already been disengaged. If I have time tomorrow I'll jack up the front end and see if the hubs are still engaged and if it still makes the sound, but I don't really know where to go from there.

 

[martin]

Check the u/joints in the ttb.

 

[exbass94]

I thought about the u-joints, but even if it was a u-joint, the hub would still be bad as well. The hub should've already been unlocked, so the u-joint shouldn't have been turning in the first place. So that means I'd have a bad u-joint and a bad hub that doesn't unlock.