I have an aluminum PC case. Whenever the metal USB plug from my external drive contacts the front, I get crackling from my speakers, which are connected to an external USB soundcard. (This crackling happens even if they're not connected to the actual output jack.) A few possibly related problems: my audio occasionally starts popping once every few minutes, and my USB devices sometimes play the "connected" sound in Windows even though they're already connected, as if they're briefly disconnecting.

My guess is that this has to do with the grounding, but I'm not sure exactly what to do. My case has a round grounding wire, but I don't know where to attach it, and fiddling with it didn't seem to have any effect. Suggestions?