About half a year ago, my Hsu ULS-15 subwoofer stopped making its usual sound. Instead, it made a farting noise, like the woofer was vibrating too slowly. It only makes the sound when it is supposed to play bass. I checked how much power it was using, and it was very little. I think it may be a built-in amplifier problem or an electrical problem. I have already tried plugging it in to another audio source and electrical source, and the results were still the same. Thank you in advance.