Front axle
 

Can some one help me out all of a suden my 1999 Ford expeditiond started making a grinding then knocking noice on the front driver side it does that after I drive it for about 5 or six blocks it does not do that on the take off . at first I tought it might be the axle boot but the axle its ok the boot has not ripped if you know something or something similar has happened to you please give me an idea on what to check .