Weird sound in engine every few seconds

Seeing as the oil pressure dropped.
Has the oil pickup tube seals been replaced?
That is a common problem with that engine.
I think also the fuel quantity valve can make that sort of noise. Although the engine tends to surge with that problem.

 

I haven't had any experience with that, so I really don't know what to tell you on that one.

I'm not a big fan of the high mileage truck. Worked for a guy with a fleet of high mileage Cascadias, and they had a lot of issues. Something was always breaking.

 

Any rotating or reciprocating part that is damaged will make a constant noise that will change with rpm. This is not constant but cycling. So it may be something like an egr or throttle valve trying to move or air compressor loading/unloading, something along those lines. I do not know DD at all unless we go waaaaaay back to good ol' 60 series days, LOL! Hope it is something easy and low cost to fix.

 

The only way I'd put a used engine in anything was if I opened it up and went thru it first. Otherwise you're just buying another problem. $15k-$18k is a great start for rebuilding what you already have.

 

Can u get a stethoscope on it and find where the sound is coming from