Hum from Subwoofers


I've noticed a hum when the volume of my system is turned up (with nothing playing).  The hum is silent when I unplug the subs (a pair of REL Storm III's).  I tried using cheater plugs on the subs, but it makes no difference.  Hum is present with the ground lifted (with cheater plugs), and present with the ground connected (without cheater plugs).  Again, when I unplug the subs, the hum goes away.
The subs are plugged directly into the wall outlets, and the rest of my system is plugged in to an Audio Magic Mini Ref conditioner (no unused outlets left on the condioner).
Any thoughts on how to correct this problem?  
In advance, thanks for your input!
Louis
louisl
Float the black wire on the REL speakon connection at the amps(Both amps)Please read REL/Support> Monoblocks (2rel) connection method.Read first and then experiment.......Good luck!!!!
Rkilowatt,  I am using a REL Speakon cable from 'Signal Cable'.  I don't understand what you mean by "float the black wire on the REL Speakon connection at the amps".  My cable only has two cables at the amp end.  A Red and a Black, terminated via banana connectors.  I have the Red cable inserted in to the positive speaker output, and the black wire inserted in to the negative speaker output.  The Speakon connector is connected to the unbalanced hi-input at the sub.
 Let me go back to the REL Manual, and review their instructions regarding connection from a mono block amp to the sub.  Again, I am using two subs.  This hum is maddening!😲