rattle at idle
 

Hi everyone, my 1998 12 valve has developed a rattle/clatter/growl at idle that I can't seem to figure out. Its more than the usual 12 valve noise and distressing enough that I've parked the vehicle. It seems to come from the drivers side and top of the engine but that's hard to really determine with all the other noise the engine makes. It goes away after 1300 rpm and is somewhat intermittent. I does not seem to effect the performance of the vehicle. My nephew suggested injectors, but I don't get any white smoke or excessive black smoke. At first I thought it might be the P-pump, but not sure about that because of the sustained performance. I tried to find it with my stethoscope, but not much luck. I've searched the forums and checked the things that I came up with such as valve train, flex plate, and motor mounts. All good. The truck has about 230k on it and I've only had it since 190k. It looks like everything under the hood is original, but you never know on a multiple owner truck. All the injector fittings still have black paint on them. I admit I haven't had time yet to look up how to test injectors or p-pump for the 12 valve. Any ideas on other things to check?

Valve lash? Cummins has used solid valve lifters up until 2019 or 2020 and the rockers sustain wear and need to be adjusted periodically. When they get too much clearance they can get noisy.

That was one of the things that I found mentioned in the forums.I checked them and it was not the issue.