Hum/Vibration in front of of '95 Explorer

So I'd like to get some advice if anyone has some. I've got a 1995
Explorer XLT 4WD with a 4L V6 and 170k. There is a hum and vibration
coming from the front end. I was told that the drain plug was loose
on the front diff and it was leaking fluid. This person thought that
problem was in the diff. Another person drove it and said the problem
was either the front wheel bearings or the bearings in the front diff,
but not likely the diff gears. What's wrong with my truck?

Here are some clues about the noise. It happens when the truck is in
2WD or 4WD. It stop when the wheel is turned maybe 15 or 20-degrees
to the right. So if I'm driving around a curve, there is no noise.
Now I know nothing about cars, but it would seem to me that this means
it's not the bearings.

Any thoughts/advice would be appreciated.

Oh, one more thing. Should I try and save some money with an
independant shop or should I take it to the dealer? I usually avoid
the dealer, but I feel like this may end up costing me a lot no matter
where I go and maybe the dealer would have an easier time identifying
the problem. Is this going to cost a lot?


Thanks all.

Jason