Hi all, i'll start off with my problem, I'm running a Velodyne Impact 12 with a Yamaha vsx-921 and after I turn off the A/V the sub remains on and every 10~15 minutes it sort of does a popping sound at rather low volume, it's actually quite hard to hear it unless there's no noise in the room. I also notice the sub does this sound if the A/V is just on and not reproducing anything, also every 10~15 minutes. Is there a problem with my system? And how do I get it to turn off after i power off the A/V? My current subwoofer is hooked up with a 5 meter cable and if i were to add another sub (with a spliter) i'd need a 20 meter cable for it, the question is should i have both subs on a 20 meter cable or is the extra distance insignificant?