It's from other bluetooth devices. I noticed that it happened only with my flip 6 (with or without party boost) and only in one specific room yet none of my other JBL speakers did this, ever. So my buddy (who's a tech genius) told me to try deactivating the Bluetooth devices and then see what happens, voila!! I was hoping it wasn't fkd up as I onky had it maybe a month, ive have it about 6-7 months now and haven't heard it unless I forget to turn off the other devices.
Hope this helps