Rear differential bolts keep loosening

Every few weeks my rear diff bolts loosen up and cause an annoying chatter at low speed. Lost one when it first started happening. I've tried the stiffest locktight I could find and it still doesn't help. Bought some lock washers but from what I've read they don't really work. Haven't put them on yet. Anyone else have this problem? Probably answering my own question but should I get new bolts as well? Had new seals put in a few years ago. Never had the problem before that.

Kept loosening with lock nuts. Got new bolts, installed with stiffest lock tight I could find and lock washers. Problem solved. Now I need to find new rubber bushings for carrier bearing mount. Checked everything else, can feel slop there.

Are you using a torque wrench to tighten them properly? have you cleaned the threads? overtightening can cause them to loosen up too and dirty threads can cause you to reach torque without the proper preload which again allows them to loosen up. should not need lock washers or lock-tite.