Hi.
Sorry if I wasn’t able to catch all of the idea discussed here.
To the extend of what I’ve learned about sound system. That kind of freaky situation might happen. It’s already mentioned about “crosstalk” (it has many of its form).
Most sound systems have various input with various sensitivities. Less sensitive input will pick up an audio signal from line out jack of any device producing sound.
“High sensitive input circuit” pick up sound signal which is low voltage, mostly microphones. This high sensitive input circuit has a potential to receive any analog audio signal transmission. It means, any device that is transmitting audio signal might interfere with your sound system. It can be a radio broadcast, wireless home system, wireless microphones, handy talki, walkie talkie, or elses.
The digital transmission will, but we all know only its carrier signal will go through and it sounds just like if you got it from any cellphone (fluttering).
When this happens, based on my experience there are some tricks we can do to fix (or even just to prove it).
- Turn off the source (if known)
- Move the source away.
- Turn off the sound system that receive the signal
- Switch the input to non sensitive input.
- Plug off the microphones.
- Adjust microphone sensitivity
- There is solution I usually do when it’s proven. (require us to have some light skill in electronics work). Open the sound system’s amplifier (some are inside the speaker’s boxes). Put a ceramic capacitor with the values of 12 to 27 pF (picoFarad) to the sensitive input terminal. One leg is soldered to the (+) input terminal, the other leg is soldered to the (-) input terminal. if it is stereo input then we need two capacitors, one to R(+) other to L(+), then both to the grounding. We avoid using higher value as it might compromise the audio quality.
That’s all I can share. If you don’t feel like to do it, let it stay as a reading supplement. But if you do, take precaution
Kevin

Edit: Other cause also a bluetooth connection which treat our PC as remote speakers (I did it from my cellphone to my laptop to scare some guys

but surely the connecting step won't work without approval connection code/passkey unless it's already paired before).