I have been under the impression that turning on and off the sound without any kind of fading is likely to cause clicking/cracking noise. Now when I tested it I don't have this problem. I guess I could have drawn the wrong conclusion the first time, it was many years ago and the noise could have been caused by something else.

I just want to be sure. Is turning the sound on and off from one sample to the next not going to cause any noise?

If I have a sound mute button in the game what is most recommended? Should I have at least some fading? How much? 5 ms? 10? 50? If I have too much the button will feel unresponsive.

I just want to be sure. Is turning the sound on and off from one sample to the next not going to cause any noise?

Yes that can happen. There are many issues that can cause a pop at the start, end, or transition to a new sound file. If the clip ends on half a wave, if it ends loudly with no fade, or if it transitions into a new sound that doesn't quite line up correctly it can cause a crackle/static/popping sound.

Should I have at least some fading? How much? 5 ms? 10? 50? If I have too much the button will feel unresponsive.

It's a good practice to end sound effects with at least a little fading to mitigate the possibility of a popping sound like that. The amount of fading is dependent on the frequency and the loudness of the clip, there is no 1-size fits all for fading.

what cch said. you can use tiny fade ins/outs at the start and end (less than 1ms) as general good practice. longer fadeouts will simulate attack, useful for some instruments (particularly brass). play around, use what works for you.