Dedicated Line Noise Filter?

@lowrider57 - @cleeds has it right- all "dedicated" means for our purposes is that the circuit isn’t being shared by other appliances, switches, lighting, etc. It reduces, but does not in my experience, eliminate, noise from other parts of the electrical system. My set up in NY (which was "permitted," but didn’t follow best practices I later learned), picked up noise from a low voltage light two floors away, and from various plug-in appliances, like a humidifier or hair dryer being used in another part of a large house. I also suffered from a nasty zap over the lines every time my tonearm  air compressor motor kicked in- this could have been eliminated by properly separating the lines rather than bundling them.

I guess the other reason why one would install a dedicated line is to be sure that you have no competition for current drawn from the same line.
I believe that the job done in TX in my new place is far better than the one in NY, based in part on the level of knowledge of the electricians, and my prodding with questions (some of which were helpfully answered by @jea48 along the way).

Tying the neutral and grounds together at the main panel is required by code and helps prevent ground loops.

Thanks, fellas. Good to know that this helps prevent ground-loops. Also relieved that my electrician confirmed his work conforms to code and matches Jea's instructions.

BTW, each dedicated line travels separately to a receptacle with the ground wire attached to the outlet...not self-grounded.

I didn't read this entire thread but I would look at a balanced power unit from Furman, Equi=Tech or other manufacturer. feed it with your dedicated line then plug everything into the balanced power unit. That should eliminate any line noise. Read more here...http://www.equitech.com/lifting-the-grounding-enigma/

@falconquest , I've been following the balanced power threads and it seems like the way to go. I don't have the funds to do it now, but I see it in my future. Would be much better than using filters and grounding blocks.
Thanks.

After much troubleshooting I can confirm that both dedicated lines are extremely quiet. My preamp is emitting a low-level hum (even through a power transformer). Swapping preamps proved that the mains had no noise to speak of.
  So I will address this issue with the manufacturer, then hopefully move on to some "black-background" listening sessions.
Thanks again to all.