Ive got an 01 gmc 2500 with a 6.0 gas. It has the usual intermitent slapping sound in the motor. Not as much since I put a quart of tranny fluid in the last two oil changes. But today was different. At accel around 30 mph the motor started to really rattle. Pulled over and restarted and gone. I revved it up from under the hood and it sounded like a bolt was bouncing up and down my valve cover. I shut it down restarted and limped it home with no noise. Now i cant get it to make the noise again and its running well. Advice? Im itching to pull the valve cover but if its running fine I doubt Ill see anything broken. FYI Im fearless but quite novice.

 

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