It is a noise coming through the speakers themselves. As many have pointed out, it is almost definitely feedback of some form.
Like back in the day when leaving a 2G GSM phone next to some computer speakers, it would make certain buzzes as it was receiving a text message or phone call.
This happened to me at work, a coworker planted a listening device in a wooden mallard and gave it to me as a gift. He was trying to collect evidence against me for attempted blackmail. I put my phone next to it and heard the staticky feedback which gave it away.
Like back in the day when leaving a 2G GSM phone next to some computer speakers, it would make certain buzzes as it was receiving a text message or phone call.
This happened to me at work, a coworker planted a listening device in a wooden mallard and gave it to me as a gift. He was trying to collect evidence against me for attempted blackmail. I put my phone next to it and heard the staticky feedback which gave it away.