On my '98 I had a tensioner pulley bearing go bad that caused a similar situation. Might want to just take it off, check it or get it checked and if it's not the problem, you may want to check the other things that the belt runs on (like the A/C compressor, alternator, etc.) for bad bearings. A good way to do this is to get a peice of metal pipe and with the engine running CAREFULLY put one end on each accessory and listen for the sound through the other end, kind of like using a stethoscope. If you do this, mind you hands, fingers, and the pipe to be sure you don't get into the fan or belt since it will be moving. Either way, definately replace the belt since it's been saturated with the WD-40. I'd get some wax & grease remover or alcohol and wipe down all of the pulleys too to get that WD-40 off while you have everything apart.
'03 XLT/FX4 L1 4x4 4.0 Arizona Beige Automatic (my weekend ride). '16 Ford Escape Titanium ecoboost (wifes ride) '16 Ford Escape S (my work ride)