Well a multimeter basically checks for voltage. You place one point at ground then choose the point you would like to test and place the other point there. This allows you to see if there are is any faulty wiring in your system. Obviously if there were complete faulty wiring you wouldn't get any sound at all.... but if a wire was poorly soldered is isn't in good contact with what it's soldered to... it could cause a glitch in your sound. Since you noted that it only makes the sound when you touch the pot... maybe you should check to see if everything is tightened down. Besides these suggestions... it's hard to diagnose electrical problems without actually hearing how the guitar is reacting or being able to see what circumstances it makes the noise. Sorry if this doesn't help you but like I said, wiring is a different story than most any other guitar problem.