It might be speaker cable-related....
I have 2 sets of speaker cables that I've tried with my 4B Cubed. Canare 4S11 bi-wired at the speaker end and a single-wire Belden 10 gauge, both from BlueJeansCable.
When using the Canare, I get the "pop" sound from my speakers on turn-on.
When using the Belden, silence.
I use the Belden.
It sounds better to me anyways.