Another similar anecdote I heard before was related to a wireless device, and some employees flying a drone during their break, generating interference.
They still work perfectly... except for a regular pop of noise every few seconds that would intermittently show up, that scaled with the volume setting.
It turned out, their portable phone (read: landline with short-distance wireless RF handset) would ping from the base station to the handset, if it were off the cradle, which was being picked up by the unshielded line-level audio cable and amplified.
Moved the base station further from the cable, pop disappeared.
But this is different than the old <2g/edge phones, which wouldn't interfere unless you were about to get a call - because the tower said "where's this phone?" and your phone would max out it's tx and say "here i am!" and that's what you heard. This is probably incorrect, but based on my observations this is what occurred.
Remember the doodads you could put on your startac style phones on the antenna bit, with LEDs in them - they'd light up when you were about to get a call, as well, by design!
And Mom ran on coffee. Lotsa coffee. Sometimes I think she just did it because she didn't hear enough complaints coming out of the speakers.
I rejoiced the day that thing died. She's now got an even beefier one, but it doesn't interfere on the 5ghz bands at all, and I'm not testing the 2.4 out of respect to the spirit of that ole menace.