I've had this problem since yesterday morning.
There are split second bits of other songs randomly disturbing the sound in Spotify - on top of my songs as well when I am not playing anything, just keeping Spotify open.
They're too short to even tell which kind of music, just enough to disturb the listening experience. It's a bit like when you used to listen to a badly tuned radio station and other signals tuned in. As much as I value a bit of nostalgia, that's one listening experience I didn't miss.
It happens with local data as well as songs streamed via Spotify.
I've got Spotify free. I've deleted Spotify and re-installed it, no change.
No other program's open. I've also made sure it really is a Spotify program - as soon as I log off, it's gone for sure.