I actually have experienced this phenomenon myself –
I had just gotten a new electric guitar ( nice Rickenbacker, actually) and noticed a very, disconcerting warbling in the upper registers. I took the guitar apart, changed strings, changed amps, etc. etc. for a few days on end. I nealy retuned the guita because I couldn;t figure out why it was behaving poorly.
It turned out that the source of the warble was the ceiling fan in my livingroom 🙁