Just a tip...usually a scratchy pot (especially those of modern manufacture) is only fixed by replacing it.

These days the old trick of blowing them with compressed air does not work much at all....The carbon tracks that are inside the pot are so thin nowadays, that cleaning is more than likely not going to fix it...

The upside is that pots, even PCB mounted ones are pretty easy to replace, just make sure you get the correct impedance on a replacement.

Dennis