Popping and Static from Speakers

[Aydrian99]

TL;DR below.

I have a problem that has me completely stumped. I have a set of reliable 2.1 Altec computer speakers that have never shown any indication of problems, except that about a year ago they started producing a popping static intermittently (sometimes every 30 seconds, sometimes every couple hours).
--The static occurs more frequently when they are on but no sound is being produced, and less often when they are on and playing the sound of a game/movie/music.
--The static frequently happens in recurring patterns, but not always.
--The static seems to have no connection to the volume setting of the speakers; the popping can be hear clearly from across the room when the speakers are set loud, or even when they are set to zero (but still powered on).
--It happens just as frequently when the PC is the only thing turned on in the room (not even lamps) as it does when there are 3 PCs, 2 smartphones, a PS3, a home theater surround sound system, a television, a cable box, and 2 lamps all on at the same time.

Figuring it was the speakers, I swapped them out for another set I had in the closet. Within a few hours, same popping static. I used these for a month or two, observing the same symptoms as the original pair. Hoping against it being my PC's sound hardware, I tried using a different 3.5mm cable to connect the speakers to the PC, and still got the same intermittent popping static (again, sometimes even in the same repeating pattern).

But here's where it gets weird: two months ago I bought a new PC, and the problem persists, with the static often in the same recognizable pattern.

TL;DR:
So in summary, I have intermittently (every 30 seconds to every couple hours) popping static that is not related to the speaker's volume, even playing loudly when the speakers are turned to zero volume, and I have swapped out the speakers, the cables, and the PC. There's nothing left to swap. Every device has been ruled out.

Does anyone have any idea what this could be? FWIW, no other device in the house seems to have any strange activity, and nothing else about the PC behaves oddly (slowdowns, graphical anomalies, etc.). No static on the home theater, no lamps flickering, nothing.

 

[Ralston18]

Patterns would suggest some regular but possibly distant source of interference. Radars, stop lights, flashing signage, etc....

Any known ham radio operators? Any nearby industries or businesses?

Or perhaps some local static build up and discharge......

Is the problem more frequent during cold, dry weather?

If you know how then check the existing power outlets for loose connections, etc. Grounding problems perhaps....? If you do not know how get assistance.

Try running a power extension cable from a completely different circuit to the location of the PC and speakers.

Try both set of speakers in another location.

Pursue the "pattern" and try to eliminate as many possible sources as you can.