So I think I may already know what is causing this (and that would be hot glue leaking into the tube sockets), but I want to ask some pros to rule out the possibility of a failed electrical component like a capacitor or something.

My stage 1 tube circuit has this odd compressed quality to the tone that releases for just a moment in a sine-wave-esque pattern when I play certain notes (G and Bb). Definitely not right, because the stage 2 tube is nice and smooth all the way across the knob.

Video (you can hear the wooOOOooo thing going on): https://www.youtube.com/watch?v=doxjexkQ-gc

So is hot glue residue in the tube sockets a likely culprit, or should I look elsewhere for this one?
Agile AL-3010SE Goldtop
Carvin 4-string kit bass
Stradivarius copy cello