Never heard an amp do this before, ideas?

@hobbes101

This may seem silly, but it can actually work quite well.

To test for RFI you can use an old transistor radio. Just turn it on and adjust the dial so it is in between stations. Turn up the volume and then use it like a geiger counter. When RFI is detected the radio will emit static.

Tony, I'm not sure the Smithsonian will lend one out. Good idea though.

Have you tried a Ferrite Ring Core RFI EMI Noise Suppressor Cable Clip, you can find them on Amazon and eBay? I had a serious issue with rfi in my system, I could hear the local am radio station broadcasts. I bought a package which included several different sizes that I was able to put on all cables attached to my amp and throughout my system. It offered me quite a bit of relief. I hope you figure out the problem, I know what it frustrating experience this can be.

When I had to live in an apartment I had an upstairs neighbor who played his stereo so loud that it disturbed my piece, quiet, privacy, and my right to choose for myself what music I wanted to hear. He bullied me with his trashy music when I asked him to stop. The landlord and the police refused to help me. My solution was to construct a microwave horn using microwave oven parts to disable his stereo. I wore a suit made of wire screen for my own safety. (Unprotected by laws and rules of common decency I did not care about the safety of my bully.) The microwaves got into the circuits of his amplifier and caused it to buzz loudly because the power supply to a microwave oven magnetron is a voltage doubling half-wave diode-capacitor system. 

Are you playing your music at a volume that violates the privacy of your neighbors? It is unlikely you have a neighbor who is fighting back if you are, but everybody who plays a stereo has a responsibility to respect the right of others to say no to music they do not want in their homes even if no law enforces it. 

Could it have anything to do with the relatively new 5g network towers?