I have a 2001 F150 SuperC at which I service religiously almost 1 month to the day after change F/R Diff and Transfer case I hear a metalic click when I take off from dead stop. I can't pinpoint it. The shift paterns on the truck have not changed. but there is a slight buuuuuuur at speeds above 75mph.

 

Check the u joints. Could be the slip yoke making noise. Remove the driveshaft and put some grease inside the slip yoke and reinstall the shaft. Seen a few do this.

Robbie