Weird sound from my computer speakers

Post date: 2018-10-07 15:08:25
Views: 8
I was sitting here at my computer this evening. I heard what sounded like a crackle (the same as what it used to sound like when you were tuning a radio long ago when the knob was dirty, a dirty variable coil or rheostat sound. ) and then a small "ping" that sounded like a system sound that I've not heard before. I am running windows 10. Nothing popped up on any of my screens (comp or phone) with any notification. More inside.

Points: 1) I do not have a mic of any kind hooked up. I do not have anything else hooked up to my computer but the speakers, screen, and through Bluetooth the keyboard and mouse. And the tower of course.
2) My new phone (Samsung S9 +) was sitting here but it does not have its Bluetooth enabled.
3) I had my browser open and a video game running in the background that does not make noise when it's not on top.
4) I have a nanny intercom but it's not on atm and I think the battery is dead on the portion near me anyway. The portion in the other room is plugged in and may be on.
5) I live near a busy street but have never heard anything like this.

Is it possible my speakers picked up a radio signal of some kind? How would they? As far as the intercom, I've never had interference from it before when it's being used.
4) I do have Bluetooth mouse and keyboard that are working with my computer.

I have never heard any interference before on my speakers.
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