rear tires locking up

I have a 2006 tacoma, 4wd, manual transmission fwiw.

Anyway, problem started a while ago with the rear tires locking up (one at a time). It happens both when the emergency brake was used and when it was not. This last time we had it towed to the shop and got it looked at, but by the time the truck got to the shop, the tire had unlocked and nothing was wrong. The mechanics have not been able to find anything wrong with it.

Just wondering if anyone has ran into similar issues or has an idea here.

 

the wheel locked up? or the entire axle locked up? were you able to spin driveshaft by hand when this occurred?