New Tube Owner

Sometimes, the pins on the tubes MAY have a slightly loose fit in the tube socket. Trust me, this has happened many times to me...don't worry, unless it happens again. Then I can take you through "the drill"!

Could have been oxidation on the tube / socket contacts, just like any other connection.

If I were you, I'd start fresh with a whole new set of tubes. That way you're ensuring maximum sound quality and not relying on the integrity of the existing tubes. I bought my amp used and almost all of the tubes were on their last legs when, to my surprise, the entire left channel cut out.

Sometimes a tube may have an internal short or bad connection. A cold solder joint to the tube socket could cause distortion/noise. Any of those problems could potentially be corrected by manipulating the tubes as you did, though it would be a temporary solution. If the problem recurs: try tapping each tube gently with a pencil. If it's a tube you can generally tell. Wiggling the tube within the socket will reveal a bad socket or connection there. If it never recurs: count your blessings. No- tubes will not have obvious distortion/noise during burn-in.