if its the clicking I'm thinking of its the actuator for the vent door. try shutting off everything off in the heater/a/c system for a couple of minutes and then turn it back on. that usually stops it for me.
The hub cap clips/mounts are damaged and allowing it to click at low speed If 4wd, the u joint may be bad.
the noise coming from this truck is the uv goints
Ford F-150 will not start all it does is make a clicking noise
Probably a cat that you ran over!
I pulled fuse on the abs system , and the noise went away. Ron
It could be a broken brake pad binding and grinding. I wouldn't drive it too far without pulling things apart and finding the source.
The coolant level is low in the truck.
The first and easiest answer is to remove the wheel covers and listen again for the clicking noise. It could be a pebble loose inside a wheel cover or a tire valve stem clicking against the wheel cover. If it's not that easy, and your truck has CV joints, I would suspect a bad CV joint. Look for a torn CV boot.
If the chirping noise speeds up as the truck speeds up, check the u-joints in the drive line.
Fresh air vent motor
Weak battery or starter motor shorted out internally.
replace heater core in a 1991 Chevy work truck 1500