Squeaking/Paper Crinkling Noise Coming from Lamm LL2.1

Thought it was a noisy tube too. Replaced all the tubes and the sound was exactly the same, so that's not the problem.

Tubes from Lamm? Some preamps are very sensitive to noisy tubes, even good quality brand new tubes. Sometimes you need to select only the finest low noise tubes and even then you can get one that doesn't work. The sound you describe sounds just like what happen in my CJ preamp. I'm out of ideas unless you have some other tubes upstream?. 

Very low noise tubes from Brent Jessee. Also, there's no way if I replaced all the tubes even with less low noise tubes, the exact same sound would be coming out. Something would change.

No other tubes. Just Herron M1A monos. 

Can it be some other electronic component like a capacitor?

Could be a cold solder joint.

Could be a dirty corroded tube socket female contact(s). Coupled with poor contact pressure between tube socket female contact(s) to male tube pin(s).

Noises are equal in both channels.

Could be the power supply, since both channels are sharing it.

Call Lamm and see?