Something, most likely in your amplifier (computer or speaker mounted) is probably acting like a radio receiver, although it COULD be earlier in the system. It is picking up radio signals and outputting the resulting audio through the speakers. The speaker leads themselves could be acting as the antenna! Try to identify the sound or voices coming out to determine what the actual source is.
The source could be amateur, citizens band, shortwave, broadcast station, or any other source of radio frequency audio transmission, including cellphones. It is usually nearby, (like a neighbor), but not always.
The next step is to find the 'antenna source', by disconnecting things one at a time until it disappears while you are hearing it. The LAST thing disconnected is where the signal is being picked up from.
This used to happen with TV's and nearby CB transmitters until the manufacturers of the tv's started installing the correct filters to restrict reception to the TV band. (Nearby transmitters, even on frequency, could 'override' the system if not blocked by filters.)
The problem is with YOUR system, or some part thereof, NOT rejecting these extraneous signals.
It is up to YOUR system to block these radio signals, NOT the 'sources' problem, assuming that the source is operating correctly.
I hope this helps!
Windows Outreach Team