High pitched screech on audio when a suspicious person got within 5 ft of my camera?

We just had a scary incident with a fake-seeming security salesman at the door, pushily asking whether we had a real security system or just had stickers up, as we kept asking him to leave. When he got within 4-6 ft of our Ring cameras, the audio became a high pitched shrill screech, like a fax machine or dial up. Did he have a hacking device on him? Is that what it could sound like? The video is uncanny, the minute he gets within 4-6 ft the audio goes high frequency din, and it goes back to normal audio as he leaves. You can hear nothing but the ring for the duration of him asking us pushy Qs about our security setup, until he walks away.