Hello all!!

I have been trying to find the source of this howling noise coming from my 2002 Ranger Sport with the 4.0L. It runs fine and idles nice and quiet steady RPMs but at speed it sounds like it is revving so high it is going to blow up. At first I thought wheel bearings but I got the front end off the ground and tried wiggling the wheels side to side and top to bottom and there is no movement at all. I did a search and found a lot on a bad IAC Valve but they experience the noise at idle and mine idles perfectly. It sounds like it is coming from the front and it really only does it at speeds over 10MPH. Another weird thing is that when I turn to the right is stops. I do have a leak around the front diff so my next thing is to check the fluid in there... I am wondering if it is low and causing the noise and when I turn right it sloshes enough oil to quiet it down... Makes sense in my mind anyway.... Any input is greatly appreciated!! Thanks!