I get my 00 GT (with 99000 miles) up to 30 mph and it sounds like a motor or something starts running at medium / high speed on the right front side. I put it in neutral and rev the engine - no change- I tap the brakes - no change-, down shift -no change-, it stays constant until I get down to about 25 and then tapers slowly off. It sounds very smooth and the sound is constant - no change in pitch or speed of the sound, it'* a droning type of sound. It does not change speed when I go faster, it just gets a little louder and the pitch does not change. It gradually got more noticeable in about one week. I checked all fluids and the levels are good, no leaks anywhere and the tranny had complete fluid and filter change last fall. Any help would be appreciated, thanks

It is very smooth, more like a whirring than humming. I guess I will have the wheel bearing / front end checked as the guys suggested. I will post the results when I get the problem solved. Thanks to all.

It was a bad wheel bearing, thanks for the advice guys. I did not know the newer ones were an assembly and not a single bearing. Makes changing them a lot easier.