Crackling Pots on V672's

Hi, a friend of mine recently asked me to add the volume/gain pot mod to the telefunken v672's he has. They are already racked. I installed the gain pots and they work great, until they make contact with the front panel. Front panel is raw steel, and is also case ground / earth, as is the rest of the rack housing. When they are in contact with the panel, they are scratchy and lots of crackling going on.

So this leads me to think there is DC on the pot? What is the correct way to solve this? I read about using a cap? Where, what type, values etc?

Thanks!

The case of a pot should not be connected to any of the terminals to control the v672 gain. If you do not have any terminals of the pot connected to the case, you have an odd problem. Possibly a defective pot?