Ampeg 4pro issue
 

I am suspecting that I have a tube going out but I want to see what others think.
When I first turn my amp on I get some crackle when notes are played and the highs of my tone seem to fade in and out. After a minute or two the problem goes away and it plays fine. It has just started doing this and its a few years old and never been abused not even gigged that much really.

It is a very good possibility. New production tubes are not as reliable as they once were.

Do some switches "pop" for a few minutes also?

That can be from DC leakage out the grid of a less-than-good tube.

Can't get it to do it right now I was playing a little while ago and it must still be "warmed up". I'll check it out tomorrow since it seems to only do it when its cold.

Ya, totally a tube on that one. I'd bag it. It'll only get worse.