Check the output impedence of the sources that you are switching. They are usally 47K. You may have to install a 47K resistor on each input line. The pop or click is caused by the output/input coupling caps. One input source will have a differance in potential/bias than the other.
hmmm. Do I misunderstand something... the output impedances of the sources is more likely to be 47 Ohms, not kOhms, and it's the input impedance of the following (buffer) stage after the selector that is likely to be 47k.
I have also sometimes problems with clicks on switches. My take on it is:
Could be capacitors / bias present; that alone would do nothing but it's the short time of non-contact while switching that confuses the following stage with an effective turn-on transient (first source 1, then no source, then source 2 connected to following stage). This is why some people use "meake before break" switches. I ain't got none of these myself. Solutions:
Have an input stage (buffer following the selector) that has a way of getting rid of the transient and/or does not lose its bias while switching. In practice, try this: measure the input impedance of the following stage. If it's infinite that means either
1a - there is a voltage follower (non-inverting) buffer with no R to ground as input behind selector. In that case put a 100k resistor from selector out to ground, or even as low as 10k. Or it could mean
1b - there is a coupling capacitor followed by a 10 k to 100 k resistor to ground after the selector. In that case try a 100 k to 1 M resistor to ground before that capacitor.
You can also try a resistor in series after the switch but I doubt it will help much, and it may mess up your gain, the distortion characteristics of the following stages, or even the filter function of the following stage, read, frequency response.
MBK
