I have my AVR sub out set to +12, it's default.  I run the 8D at around -3.  I have the crossover at 100 in the AVR.  I have the sub EQ set to narrow, 80Hz, and -5db to handle a positioning problem.  I get no noise.  If I have the volume on the AVR high with no source on and put my ear within a foot or two a hiss is audible but can not be heard at all a few feet away.

I would suggest that you take great care with the cable placement and quality, test your house wiring (many homes, including new construction have ground problems), and bump the AVR sub volume up as high as possible.

Cheers