Are you saying that you ran a separate 12 guage ground wire in parallel with your 20amp 12 gauge Romex? Did you leave the Romex ground wire unconnected? (Because if you didn't you'd have a ground loop.)
How to guarantee to lower noise- ground loops in your system
I have been through many problem area where noise in the audio chain was a problem.
my friend Who is a Electrician solved the problem . All too many times people add a dedicated 20 amp circuit 12awg is standard 11-10awg even better lower resistance , also most important
you need a Isolated dedicated ground, this is totally insulated right back to the earth ground in the
breaker box this will dramatically lower your noise floor and remove ground loop problems .many people just put a dedicated line and think
that’s it ,not so, if you are going to go through the trouble, then for maybe $100 more the isolated dedicated ground to the dedicated circuit is a must. I can tell you without question .
my Audio has a noticably quieter background .in songs i now hear low level musical artifacts like reverb off a guitar fading cymbals and clearer seperation of instruments .well worth the effort .Hopefully
this will help others .this is a essential system upgrade .
my friend Who is a Electrician solved the problem . All too many times people add a dedicated 20 amp circuit 12awg is standard 11-10awg even better lower resistance , also most important
you need a Isolated dedicated ground, this is totally insulated right back to the earth ground in the
breaker box this will dramatically lower your noise floor and remove ground loop problems .many people just put a dedicated line and think
that’s it ,not so, if you are going to go through the trouble, then for maybe $100 more the isolated dedicated ground to the dedicated circuit is a must. I can tell you without question .
my Audio has a noticably quieter background .in songs i now hear low level musical artifacts like reverb off a guitar fading cymbals and clearer seperation of instruments .well worth the effort .Hopefully
this will help others .this is a essential system upgrade .