Brian, good info - thanks! To answer your questions:
1. One amp is 10 years old (Suhr Badger 30), the other is 51 (Fender Princeton Reverb)
. I can also get the noise with a line6 Helix, so its not necessarily due to tubes and electrolytics.
6. No, I only bring them to top folks in the area.
I'm going to go through a full debug session on Sunday - turning off all other breakers, running the amps from battery, etc so I can try to narrow it all down... I'll post back with what I see.
1. Same interference on 3 different amps from 3 different eras, all 3 with not input?
a) If the hum coming out of the Amp's speaker where you placed a microphone in front?
b) Can you hear the hum directly?
c) If you took the amp to a different location, like a different house another part of the city, will they still hum?
d) Do you have high tension power lines within 2 blocks of your house, or, a transformer power sub station within 6 blocks of your house? (If the answer to this question is yes, you are most likely out of luck, sorry.)
e) Do you have access to borrow a (I hate to say this) a high end power line filter and isolation filter like those used by some adiophiles? (These weight quite a bit as they have 2 large transformers in them with huge caps) I'm not talking about those cheap power filter bars or boxes.
6. g) Are you saying all of your amps have been serviced?
NOTE: A deeper look at your .mp3 file revealed perfectly timed diode switching noise in the waveform. This may be due to light dimmers always on at the same brightness, computer/electronics power supplies, LED/CFL lamps, or, on your power grid, even street lights, or someone has a huge device which internally operates electronically with DC at the full AC mains voltage.