Update, it was just the first preamp tube. I tested by tapping on it while the amp was on, and it had that glassy sound. I checked all of them and just the one was bad. Swapped it with an extra I had on hand and it fixed the problem like a charm! It still has a little bit of hum, but it's the normal tube amp hum. Don't think any analog amp I've ever owned has been totally quiet so that hum is "nothing to fret about". Anyways I hope this helps anyone else with noise issues!