Binding/growling/grinding

When you go around curves or make turns you hear this, what some call a binding noise. Now starting to feel it under your feet. Seems to do it after the truck has warmed up. Notice it more if I'm pulling a load. No one has been able to locate problem. I had the differential changed out, as we thought there was play in spider gears. Another shop said, there was nothing wrong with my diff, but the front end had worn parts. Got those replaced. The problem is still there and unfortunately is inconsistent. Motor mounts are ok and tranny was look at and minor repairs done.

Driving 50 mph, now feel that something is shifting under the truck, like a back & forth movement. Mechanic can hear metal to metal when shifting from "R to N", but truck is so loud it's hard to tell where it's coming from. Please help! I am at my wits end and don't have money to tear into this thing.