Recently my powered sub started making what can best be described as a crakling noise. I adjusted the gain and it had no impact on this noise. I then disconnected the RCA cable and it still makes the sound. I shut off the stereo and the sub still makes the noise. The only way to stop the noise is to unplug it from the wall (power). Any ideas? Is it receiving interferrence somehow? Could it be our wireless internet? We recently installed it but didn't notice the crackling subwoofer until the following week. Thanks for any help!