NS-10 noise and hum

[elevateconsulting]

I have been trying to isolate a hum in my NS-10s. I have my balanced monitor outputs running from my Apogee quartet going to a cheap QSC power amplifier, the outputs of the power amp are going out unbalanced to my NS-10s.
When I turn on my amp i get a low hum and what appears to be some noise from USB. I went to the local electronics shop and bought a consumer grade Ground Loop Isolator. I placed this unit between the Apogee outputs and my power amp as suggested and it did remove the USB noise however the low hum still exists.
When the Apogee is outputs are disconnected from the Power Amp the hum is still there so that makes me believe that the hum is coming from within the power amp itself.
What i did was take the unit and put it between the Power Amp outputs and the NS-10 speakers. That completely removed the hum noise however it appears my output volume is being attenuated as well, as I can't get nearly the output volume coming out the power amp as if I was running straight to the NS-10s without the Ground Loop Isolator in between.
From what I can guess the noise from the Amp is coming from an issue within the Amp itself or because of a poor grounding issue coming from my house power.
Can anyone tell me why the Ground Loop Isolator would be attenuating my volume from my power amp and if they have any suggestions for a different fix?
Thanks guys