I have a terrible grinding noise coming from the front end. Sounds like metal grinding, it fluxuates with speed, it feels like it's coming from under my feet. The 4 wheel drive sounds like it wants to lock in gear, when I lock the driveshaft into 4 wheel drive the noise goes away. When I unlock, it comes back. I had the hubs checked, they look fine. Could it be the rear, 4 Wheel drive, Does any one know? Please Help!!!!!!!!!!!!! 1999 Ford F-250 super duty pick-up

 

it sounds like its not disengaging all the way...has anyne put it in the air and run it to check?