Loud Screech starting up

[smallmany]

I leave my headphones plugged when I start my amp, and I noticed it makes a sound like a nail is being scratched across a blackboard.
Is this normal

[smallmany]

Amp is not connected to source and at quarter turn on the pot when its fired up.

[Paul Birkeland]

Does this only happen when it warms up?

Some tubes will sputter just a little bit while warming up, this isn't particularly abnormal. 

[kscwuzhere]

I used to have an extremely loud popping/crackle sound when plugging in my headphones and solved the issue by checking the grounding path and making sure that I had no cold solder joints. After I found which ones did, I re-soldered and the crack was back to normal. There's a sticky thread about the Crack's grounding path, I'd check that out.