Help . Been fiddling over the last couple of evenings to get my sub crossover exactly right. Have got my speakers all set to small, crossover at 80hz, and 80hz crossover on the sub. After reading a couple of posts on here, I experimented with "disabling" my crossover on the sub (by switching the crossover to maximum until it clicked) and letting the Marantz do all the bass management. However, when I do this, I pick up a noticeable hum which can be clearly heard when seated in the sofa next to the sub. With crossover at 80hz (or any other setting apart from 'max') there is no hum. Is this a sub issue or is there something wrong with my amp? Any advice appreciated.