I drove my 90 Burb to work the other day and I had this odd feeling,almost like I was towing a small trailer,I hadn't noticed it before and figured I'd look at it on my day off, well after I got off work I took the kids to school and on my way home I turned a right corner and BAM this loud noise came from the rear end and slightly jerked my truck, once I straightend out the noise went away,and never came back mostly all left turns back to my house until I turned on my street,right hand turn another loud bang and some fairly hideous grinding noise until I straightend out again,I'm thinking something in my rear diff is broke,any other general thoughts?
Change the differential fluid ASAP. Could be the locker is just hanging up. I like the LUCAS brand, but there are lots of alternatives like Royal Purple, Amsoil etc.
While you have the cover off, any debris in the carrier will indicate trouble. Otherwise you should be good to go. If you've never done it yourself before, here is a great pictoral how to: http://www.stu-offroad.com/misc/diff-1.htm
I agree try changing the fluid. I recommend AMSOIL sever gear, it has the slip lock additive already built into it and should help you out. AMSOIL 75W-90 Sever Gear
A study of automotive gear lubes. Use this to decide what lube is best.