Screeching amp noise

[leib10]

It’s only intermittent and seems to happen more when the amp is just turned on. Any ideas about what it is?

 

[glpg80]

Is there anything in the effects Loop?

 

[leib10]

Is there anything in the effects Loop?

Yes, just a delay pedal. But the effects loop isn’t active when it happens.

 

[TheToneDig]

Did you go through the usual checklist of power cables and if tubes that they are seated properly in and maybe replace V1 to see?