I noticed tonight that there is a loud "whirrling" noise coming from my engine bay. So I keep the truck in idle, pop the hood, and listen. Check around for a little bit, crawl under the truck, and notice that it seems to be coming from the lower pulley. Everything looks tight, couldn't see anything wrong. The pulley is an aftermarket 4# (don't know the brand, came with the truck). Anyone have any ideas as to what it is? I have no other symptoms besides the noise.......... :shrug: