I'm stumped as to what the root cause of the dull thumping noise coming from the front end of my 1997 Ford Explorer XL...

For anyone that can help, here is what I know..

The noise is a dull thump, like a heavy gauge piece of steel under pressure being smacked with a hammer. It thumps with every rotation of the front wheels. It does not matter if I am in neutrul or drive nor if the 4 wheel drive is engaged. If I jack it up and spin the wheels by hand there is no unusual sound. The only thing I've really done is a visual on the front end and everything looks good.

I'm guessing it's a bearing problem because it only happens under pressure but I'm not swapping out a hub without someone else's opion first.

FOR THE LOVE OF GOD, HELP ME!!!!!