Gain controls, which utilize a variable resistor called a potentiometer (pot) to control the level of the input signal, can collect dust and other particles inside of them. A common symptom of dirty gain controls is an crackling, static, or intermittent sound when adjusting the gain control. This problem can sometimes be remedied by spraying an electronic contact cleaner spray on the body of the potentiometer to enhance electrical contact of the sliding wiper inside the housing of the potentiometer.
Confirm the potentiometer is causing crackling/static/intermittent sound
Clean the potentiometers with an electronic contact cleaner spray
Important note: If this procedure does not fix the issue, check all upstream audio devices in the audio system. If all other audio devices check okay, the gain potentiometers may have to be replaced with brand new ones. Please contact a QSC Authorized Service Center for repair options.