I have pops when all channels are in 10W. And sometimes on other wattage too.
And I am not talking about going from and to 10W like explained in the manual. So I assume they may be abnormal.
I have discovered that they become less powerful when I cycle the channels in higher wattage (45w or 90w) with the amp turned on and not in standby, then come back to 10W. They become softer but still there.
Since it cannot damage the amp in anyway, I don't bother too much for now, hoping that a new set of tubes would eventually fix it.