This could actually be a belt tensioner..... I would remove the serpentine belt and start the engine for a min to see if the noise is still there. If not, its an accessory, if it is, then its internal.
Modular motors builds some sick 4.6 bottom ends and motors. ... Maybe them.
I gave up the whole idea of a SC on the adren.
I built a Whipple F150 instead....
Blead / Burp the air properly ??
Is the level 100% full.
Check the heater control valve function.
Could be the Check valve in the vaccume line on top of the computer under the hood.