Only a tick here, so I would say a plop isn't normal without putting much significance to it when you said it's not loud. Maybe it depends on the speakers.
Why would you first turn off the devices upstream, that can only cause more glitches.
And one dealer (he doesn't sell Bryston) told me that it's better when it ticks (or plops), that means that the signal path is not crowded with the relays or something like that.
