What's the sound???

After driving my truck for varying durations, 5 minutes to 200 miles, I will hear a…Pung! Imagine the sound a pop can makes when you pop a dent out from the inside. But imagine that sound with steel rather than aluminum. I cannot pinpoint where it is coming from. I've thought it sounded like the exhaust or maybe even the fuel tank or maybe even the drum brakes. All I do know is it comes from behind the cab of the truck. I can't make it happen repeatedly. I just have to listen for it….and jump out to see where it's coming from. <sigh>

Sometimes the truck will be running when I hear this sound. Other times I will be walking away from it after I park and hear the sound.

Truck is a 1997 C1500, Ext Cab, 2wd L31/auto w/192k miles.

Any ideas where to look or even how to figure out where it's coming from?

Not much I can think of except the exhaust system. Any change in performance when this happens?

Nope. No change. I usually only hear it once I shut the truck off, though I have heard it while driving too...

If you mostly hear it when the vehicle is cooling down, It's probably something contracting. Maybe a baffle in the muffler? Doesn't 'sound' like any to worry about. Just one of the charming things your truck does.

Sounds like maybe the heat shield on your cat conv.Maybe your gas cap is not venting.Good luck!!!ACE

My '98 used to do that too. I would always notice it after shutting my truck off but would occasionally hear it while driving like sitting at a light. The conclusion I came to was the exhaust cooling down and the metal contracting as it cools like rustycarz mentioned. Nothing to worry about, like you said it does'nt change the performance at all.