Anyone have this turntable issue?

Whenever I set my cartridge on the record, I hear a loud pop. This is with the volume turned down all the way. It seems to be the stylus entering the groove. I have done everything to avoid static in the system. I'm quite sure it is not static. Just one loud pop when the cartridge is lowered. No problems after that. I cannot imagine how that impulse noise gets to the speaker with zero gain on the preamp/processor. How can this happen?!
Find a cheap pair of headphones and plug them into the headphone jack. 

Just don’t have them on your ears when you “drop the needle” 

just an idea that the optical encoder is causing the noise, and most probably needs attention, check that all its connections are firm on the sub board and then to the main board . I am not sure that optical encoders when at min mute the signal, that’s why your problem is solved when mute is on. Do you have too much gain?
Got it solved. Too much gain. Turns out there is an analog trim in the Bryston that needed to be engaged. Thanks for all the suggestions!