When you changed the trans fluid did you change the
filter too? Or did you have someone do it? You should
really drop the pan and clean the magnet and change
the filter if you haven't.
To check your rear diff fluid use a breaker bar and
stick the end of it in the top plug and reach your
finger in there and if it's almost right at the top at
least you have the right amount of fluid. Check the
fluid with a white paper towel and see if it's black.
If so, go get some new fluid. Drain it from the lower
plug and fill it through the upper plug. Put it in til it
just about overflows out of the top fill port. That's
how I've always done it. When you fill it, fill it with
75w-90. I personally put the severe gear oil from
Amsoil in it. This would be the cheapest place to
start if you find that it's not a wheel bearing.
Either way, not a bad idea to change out your
front/rear diff fluid regardless.