Hi, after reading about your problem I have some suggestions. I am assuming you still have the noise with no cable connected (a cable plugged in only on one end will pickup RFI noise like an antenna). I am also assuming that you have tried the sub on different outlets/circuits and still have the noise (if you haven't please do so).
I have a similar noise on my AC with my Mirage and Energy subwoofers. I don't have the noise on my PSAs or Acoustic Research subs (all have ICE amps). All of my subs have two prong power cords so cheater plugs won't change anything. In my case it is harmonic noise on the AC that is not being filtered by the subwoofer power supply (Mirage/Energy). By turning the crossover dial you are first, engaging the crossover (it is off in the full clockwise position). Second, as you turn it you are filtering out the 60Hz 1st harmonic at 120Hz. The PSA subs have wide responses so several harmonic octaves can be amplified and heard through the sub.
* When crossover is not engaged does the noise change when you touch the amp or RCA connector sleeve with your bare hand?
* Does the noise change if you touch a conducting wire between the outlet screw (earth ground) and RCA connector sleeve?
* Does the noise change at all if the subwoofer is within 6ft if the receiver/preamp with a 6ft it less interconnect?
If you hear changes we should be able to fix the problem simply. Please report back. If no changes I suspect a defect in the ICE amplifier.
Personally, before I do anything I turn the amp volume up to max with no interconnect to listen for AC harmonic noise. Then I connect the interconnect to the preamp (muted) and listen again for harmonic noise (ground loop). Again with volume up to max. This ensures the lowest noise floor before I start tweaking.
Try this link for my full story in regards to getting rid of my noise in the rear subwoofer:
Sent from my SM-G935V using Tapatalk