I suspect you are adjusting the fader in an input card. This is a stepped control, it moves in 6dB steps. That is the noise you can hear, the click as the gain steps up and down.
It is generally not desired to have user control of such input gain. If you require a linear control, use a gain object. No operation noise will be heard.
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It is generally not desired to have user control of such input gain. If you require a linear control, use a gain object. No operation noise will be heard.