Yesterday morning I was pulling onto a main highway, and had to apply added right foot pressure to fall in line with traffic. I was also pulling a 6,000 lb. load at the time. During this time I sensed something was either broken or just let go in the rear differential. Shortly after, I started hearing a growling noise that would come and go under differing conditions. Sometimes I would hear it during acceleration, sometimes going around a bend in the road, and sometimes when I hit a rough spot in the road. By the time I got back home later last night, the only time it was evident was under low speed acceleration. I suspect carrier bearing, but maybe pinion bearing. I would imagine this kind of thing has happened to others, so if you have any thoughts on this one, please share them. BTW there are no leaks anywhere. Thanks in advance.