I had to steal the pre-amp away from my Stanton because the BSR's ceramic cartridge seems to require the special 470 ohm impedance setting.)
Ceramic cartridge? If memory serves me right a ceramic cartridge does not need a phono preamp. You should be able to connect the cartridge to just a line level input on a preamp.
Try that and see if that helps the popping sound from the switch.
If the popping sound is still heard you can put a snubber circuit around the switch contact. It consists of a capacitor and resistor in series, paralleled across the switch contact.
Post back if it still pops using a line level input on the preamp. Somewhere I have the info for the values for the cap and resistor....