I've had this Polk 6000 Soundbar with Wireless Sub for over a year. Yesterday the sub started what can be best described as pulsing. It is a very low sound frequency, short pulse occurring every 1-2 seconds. They do not match any sound inputs occurring on the soundtrack of any tv show or DVD. It occurs on inputs two and three. It does it while plugged into different electrical outlets. Does anyone have an idea what is causing this and how it can be fixed?