I've only had the truck for a few weeks. It already had the tunes when I got it. It just now started getting cold enough for the truck to idle itself up on warm up. If I turn off the turbo brake it totally disappears. This is the 3rd time I heard it do it.

The first time I heard it I was inside my house and heard it happening through the wall! I was afraid my heater grid bolt broke off and got on top of a piston for a second until I realized what was going on.