I took truck to carwash(selfserve) its winter and very cold. I needed to get salt off the frame. I drove home, all was well. 5 hrs later I went to store, on the way my truck made horrible grinding noise.....so I switched to 4x4....the 4x4 works, and noise goes away...so i switch back to 2wd and its ok for 10 seconds, then grinding. nothing lead up to this, no warning. its an 05 f150 4x4 4.6l automatic. 4x4 is manual stick. help whats wrong plzzzzz.