My favorite amp a 5e3 homebrew has been giving me fits. Notes are crisp on attack but get fizzy as they decay. I've changed tubes, and used cleaner on the pins. Plugged amp into a different cabinet, and plugged speaker into a different amp. Looked for cold solder joints, and chop sticked around. Have not found any trouble spots or any problems; it's getting a bit frustrating. I can't remember how long ago I built it. Perhaps it's time to put in new filter caps not sure what else to try at this point~arghhh!