My audio setup is a bit older, but here goes: Yamaha mid-90s receiver (no DTS, just DD) and a Polk sub woofer from early 2000s. They are connected via. The sub works, but there is a constant "hum" out ...

The sub should not hum. Can you hear the hum in a quiet room, or do you have to have your ear right up to it? On really low end stuff, it may be normal, but if I were you, I wouldn't accept anything ...