It depends how loud the humming is. LOL. Sorry about that but amplifiers hum because of the filter circuit is not enough. Second, wires are too close to output or input connectors. Third, not using a power strip this is also known as a surge surppressor look alike units. The most common hums is from ground loops.
You can try open up the subwoofer and move some wires around, but be careful while doing this. You can improve the filter by putting a higher capacity capacitor. For best performance the filter should have about 20,000uF when using a non-regulated power supply. Try to use shielded wire for all inputs.