My 2006 F-150 has 8,900 miles on ive noticed in the past month and a half that there is a weird grinding noise coming from underneath. i sent it to the dearler and they checked the all the fluids out and put the computer on it and everything came back fine, they didnt hear the noise at all and i told them it only happens once in awhile. i also noticed when it starts making the sound i have to slow down to about 10 or 15 mph for it to stop and when it does it sounds like something is clicking into place. if anybody can help i appreicate it. its an 06 F-150 4x4.

 

If I remember right, I had one doing the same thing at the Dealer I work at. There is a TSB on this concern. It has to do with a small solenoid on the firewall that loses vacuum and causes a 4X4 hub to slightly engage causing the noise.

Well, I just checked. It must be a "Special Service Message" on this matter. PM me with your VIN# so I can find it.