Does anyone know what could be causing this? My Sonos Play:5 1st gen makes this repetitive sound in the video over and over with all my devices EXCEPT my Audio Technica LP-120 turntable.

I've had it for about five years, initially only using it with the turntable, and knew the sound was there because if I was sitting near the speaker with no music playing I could hear it faintly (especially if I put my ear up close), as if it was coming from inside the device but not out of the actual speaker almost. But since the sound was always so faint and never seemed to come through the actual speaker when I was playing my records, it never bothered me. 

But recently, I bought a vintage Technics cassette deck (M205) and receiver (SA-222). And when I try to play music with either the cassette deck or the receiver hooked to the Play:5, the dit dit comes blaring through the speaker with the volume the way you can hear it in the video (the video is the quiet part between tracks on a cassette to avoid copyright issues, but it's quite audible over the actual music, too).

I know it's not the cassette deck or receiver, since it was making this sound faintly on its own before them, although I'm not sure why it blares the dit-dit when they're connected but not when connected to the turntable.

Any idea what could be the issue and how to solve it? Thanks!

Sonos Play:5 Makes Repetitive Dit-Dit-Dit Sound