actually the harmonic is the 3.2 fret harmonic, which on the E string is a B, two octaves above the B I'm playing on the A string. It makes sense that the B would induce a harmonic of the same note, but I'm a little baffled it can sound through my mute. The harder I press my palm mute the strings, the more audible it becomes. My palm is slightly off the bridge, nowhere near the fulcrum position. It should kill everything.
I can only guess that a lower frequency vibration requires more amplitude which my mute destroys, but a higher frequency vibration requires less amplitude, which allows it cut through. This may explain why I'm getting the 3.2 harmonic rather than the 7th fret harmonic, which is also a B but an octave lower.
Here's another piece to the puzzle. The room I usually play in has a node (or anti-node?) that causes B notes to create a resonant peak. I thought my monitors were garbage at first, but it's definitely just the room. I get the ringing harmonic when I'm in headphones and have the monitors off, so the only resonance from the room would have to come from the acoustic noise from the guitar, which shouldn't be enough to cause any feedback, especially with a mute. I feel like the induction is coming from the vibration of the guitar itself. Nonetheless, I need to test this in another room just to be 100%.