Hey. I been having the same problem for a while. I even went to the store and they replaced my old speaker to a new one. And guess what?
The same problem keept happening. So I'm assuming is the phone. But u have tried so many options. Bluetooth ,Aux, Turning the WiFi off and on, using diferent source of music. I have tried different phones and computers and nothing.
The only thing I have noticed. Is that when I play my music very loud the problem goes away. (That's a problem for me because I love music. And I have bought that expensive equipment so I can listen good quality songs)
And plus not always you want to listen to music that loud.