I have a 1998 f150 4.6 4wd and while driving there is a grinding noise, not a horrible noise but higher pitched coming from the front end. It happens after I stop usually but sometimes just happens while driving. If I hit the brakes the noise goes away, then when I release them it happens again. Speed doesn't matter either. I thought maybe it was something to do with brakes/rotors but I checked them and they are fine and rotors have no scratches. Any ideas?