For got to ask in previous reply. What engine do you have in your truck? I assumed it was a diesel by the thread that you posted. But I see by you having an air pump it is a gasser and most likely a 5.7L Gen 1. What you can do though is remove the serpentine belt then run the engine for a short...
I would first remove the serpentine belt and make sure that your pulley and Balancer are not failing. Both produce a clanking noise when they have started to fail. Engine damage will result like a Broken crank.