HTS10 with pulse heartbeat

I have an hts 10 with a distinct low thumping 140 bpm pulse. It continues even if I disconnect the lfe rca cable, and continues when there is audio playing, though the relative volume is low. What does it take to get this fixed? I'm doubting a firmware update will fix this. Is Polk willing to send a new amp board? I'm handy with electronics but I would love if Polk stepped up here. Thanks!