EZ 1290 build question

[Mxc7976]

Hi all, I’ve just finished up my 2 channel 1290 build and it is working and sounding great. The only issue I’m having is channel 1 makes a popping noise when I turn the gain knob. This does not happen with channel 2. From what I can tell the two channels are behaving exactly the same otherwise.

Any ideas what this could be?

 

[3nity]

Maybe a cold joint ?