Squeak sound after rebuild

[edekok90]

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

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[ikuo78]

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

 

[edekok90]

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

 

[DadOSix]

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