If the switch used is not a type called 'make before break' (where the connection to the new position is made before the old position is released) then it is quite normal to hear a bit of a pop or click between positions.
However- in audio applications it is a standard practice to use a 'make before break' switch in volume controls and selectors.
Other things that can affect popping or noise in the switch:
RF from your sources (digital noise can do this too)
DC coming from a tube that has internal leakage or a short.
If a tube has some slight microphonics it can also ring or react slightly when the switch is moved. If this is the case moving the switch very slowly and deliberately will prove this out.
However- in audio applications it is a standard practice to use a 'make before break' switch in volume controls and selectors.
Other things that can affect popping or noise in the switch:
RF from your sources (digital noise can do this too)
DC coming from a tube that has internal leakage or a short.
If a tube has some slight microphonics it can also ring or react slightly when the switch is moved. If this is the case moving the switch very slowly and deliberately will prove this out.