I stopped for fuel this morning and the shop owner asked me to listen to his 2004 truck, 5.9 cummins, at idle it sounded like a dry rattling under the valve cover, almost like sticking a stick into an electric fan blade. He figured a piston noise but it was too fast for that at idle. Sounds like something in the valve train to me. any ideas on this ?

 

Did the noise increase speed with increased RPM?

 

yes it increased rattling speed

 

Valve seat drop? broken rocker?
I would start by taking cover off and see if you can see anything obvious.

 

Had a very similar thing happen on my 04. Wound up being a broken ring on #6 piston. Took out a chunk of the cylinder wall and ended up on top of the piston. Had to scope all 6 to find it. Ended up with a total rebuild.

 

False alarm,, it was torque converter loose, tighten bolts now all quite. Thanks for suggestions.