My 06 TB mostly gets driven on the weekends. Last weekend there was no issue, however yesterday we took it out and noticed a distinct howling, which sounds to me exactly like it has big mud tires on it. Seems to come from the front end. Sound starts as soon as we go over about 20 and gets higher in pitch as you go faster, then slowly comes down when I slow down. I can feel a slight vibration in the steering wheel and pedals. We were on our way to have the oil changed, so I had the tires rotated and checked for any slop in the wheel bearings. Everything feels real tight, no movement at all. Checked the tires over real close, no chopping, wear looks good, 24000 miles on the Goodyear Wranglers. I had the front diff fluid level checked, all good. Fluid is good too, I switched it to Royal Purple about 3000 miles ago. On the way home the sound was still the same, still seems to be from the front. I was curious if the sound was in the drivetrain, so I put the truck in Nuetral at about 60, no change at all in sound. Engine sounds great, and no other symptoms aside from slight vibration and the sound. Any ideas what I could try to diagnose this?