The noise seems to only occur after the truck has been sitting overnight and has cooled off completely. It will not occur if the truck is restarted after already being used that day. The cold temps definitely has something to do with it. The heater is in the defrost position and the fan is on low. I'll try it with them off tomorrow morning and see if there's a difference. I didn't notice this sound last year, but I kept it in the garage. To me, it sounds like something isn't getting lubed on startup.