For those that have this chirp sound, have you tried going under the truck and shaking the exhaust system. Perhaps its one of the exhaust hangers or heat shields. I know my truck has a heat shield vibration on idle every now and then. I've been under the truck and tried to fix it. I got it to stop temporarily but now it is back to vibrating again. Next time Im in for service, I'm gonna have them look at it and see what they can do.