Sound of rocks in exhaust

If your truck is equipped with a catalytic converter as part of the emission control system you may be hearing the material inside coming apart, happens with age, it plugs up then exhaust pressure causes it to break apart and it will rattle around in the resonator. It could also just be some rust flake that has come off inside the resonator (muffler), either way it usually is something internal failing in the exhaust.

 

Maybe you upset someone and they put some rocks in there? Un-popped popcorn is more entertaining though.


I agree with brian, probably a baffle or something inside the muffler broken off.

 

The cheapskate owners at the oilfield services company I worked at wouldn't put more than a 1/4 fender on the trucks, which left a big gap before the front of the trailer. In the heavy mud of the lease roads the tires would coat the back of the cab, and even throw the stuff into the stacks.
So, it may well be a rock. Get a band clamp, undo or cut off the one at the bottom of the stack and have a look.

 

Is this a little C7 or C9 cat? I've seen a lot of the turbo waste gates come apart and rattle in the exhaust. Didn't seem to change power or the way it ran any. But when we pulled the exhaust pipe to find the rattle, we found a little black button thingy about the size of a nickel. It was part of the waste gate.