rattle with engine under load

I've seen this as well when an engine miss is present. The engine miss is transferred to the trans by interrupting load on the trans and the mainshaft gears rattle and jingle.

 

I would take it to a good N-14 mechanic that has all the tooling to find the problem and is willing to follow your lead in the repair, not one that wants to tell you nothings wrong with it. I wouldn't put it off too long.

Have you noticed even a slight power loss with this noise occurring?

 

Ever get it fixed?

 

First off the valve covers being Red is an option it has absolutely nothing to do with the engine HP or Torque. It is not a coded message, just an option.
You can get the original CPL and numbers from the original equipment truck dealer. Everything else will be in the ECM program.

 

Meh, drive it until something grenades. You'll find the problem then

Try pressing on the clutch lightly while it's happening and see if it changes.

 

A while back I had a rattle I couldn't put my finger on for a long time. I have a 08 Pete 389. Turned out when I finally found it, it was the bushings on the clutch linkage was worn out. I would only hear it under load. Never just cruising along easy or at idle. but as soon as I put a little torque to it the rattle would appear. When the rattle becomes apparent next time just rest your foot on the clutch a little and see if it stops. Just a thought.

 

Friend of mine wrenches on cars in his own shop, he has a test tool with wires and probes of some sort he can attach to the drive train i think he puts the wire and the sensors out the window and Velcro's it on to the car where he thinks the issue is an then he can narrow the source of the sound when he drive down the road and then finely finds his issue. MAYBE you could talk to the car mechanics in your area an see if they have a tool like that. or even if the diesel shop does