I went to run errands the other day and experienced a weird ticking noise before I got out of the neighborhood, so in case it was something important, I came home. It starts at around 30mph, frequency increases with speed and cannot be heard with the truck parked and increasing RPMs. We had a ton of leaves recently and I was hoping there was one stuck somewhere We pulled the two covers on the firewall and blew a ton of leaves out. Drove it again and ticking seems maybe a bit quieter, but still there, still starting around 30mph. Any ideas what else to look for? My husband asked if it ran hot at all, but I never got it far enough to get it up to temperature. Truck has about 253k miles on it and starts easily, runs great.