Remove your belt and then spin things buy hand, do they make any noise?
With the belt off start the truck and then rev the engine over 1500 rpm a couple of times, does it still make the noise?
I must add, DO NOT let the truck over heat while you are doing this.
Only run it for a few minutes and with the heater on.
The "Storm Trooper", 1997 Discovery with 245,000 miles, still a daily driver.