Every now and then I get what sounds like internet radio or some other website transmitting an unwanted signal. I've also noticed heavier spam in my email.
No, I'm not close to any of that, and it stops when I log off, which I usually do to get rid of it. But then it eventually comes back. It sounds like internet radio.
There are components on a system board that will behave like crystalss or a tuner if the signal is coming from the right direction at the right broadcast frequency... See if it changes when you move your computer around.
There is nothing you can do about it, but it is not necessarily harmful... you can complain to the FCC and they can fine the offending party.