Squeak sound after rebuild

Have this strange squeak from oil fill cap. Bottom end was rebuilt 800 miles ago. Only is noticeable when engine gets to operating temp. Any ideas on what it may be? No CEL or engine lights. Took belts off to rule out pulleys

It's about 1/2 cycle of the motor rotation speed.
Is it a rocker arm?

I haven’t had the chance to take the valve covers off yet

Pcv valve. Check and see if you have suction or pressure on that oil filler. Should have a slight draw (suction).

DadOSix said:

Pcv valve. Check and see if you have suction or pressure on that oil filler. Should have a slight draw (suction).

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I’ve changed the PCV valve thinking that could be the case but nothing. Still has the same noise

Maybe try a mechanic’s. Stethoscope along the valve cover on each cylinder and see if you can isolate the noise to a single cylinder, which it sounds like just one. With the bottom end rebuild, I would be thinking that I have a pushrod / cam lifter isssue. The older 04, 03 and 02 had huge weep holes in the rockers that do not keep enough oil on the valve train. They spew oil all over the engine bay when the valve cover is off. When my 04 tossed its’ cookies one winter, he got all new rockers with the smaller hole (and better design) to keep that oil where it belongs.

A thought - with the filler cap off, the sound should get faster as engine speed increases. Does it ever go away (at like 1500 rpm)? A higher rpm would push more oil thru the system.