I hear a "pop" too, but my situation is different from yours.
My cable box (Pace RNG 110) is connected to my BV10-40 with HDMI only, and when I used to have only front speakers (BL 9) connected, would not hear a "pop" when changing channels. Recently, I installed rear BeoVox speakers through a Beolink Passive amplifier. Now, I hear a "pop" from the rear speakers when changing channels. Strangely, I hear the "pop" even when in speaker 1, 2 or 3 mode; the Beolink Passive amplifier stays on no matter what speaker mode.
It has gotten annoying enough to the point where I sometimes unplug the Passive when not planning to use surround sound.
Leo