Dedicated Line Noise Filter?


I don’t know if what I’m seeking exists, so I’m asking the experts.
I have 2 dedicated lines installed; one for analogue, one for digital. They originate at a sub-panel off the main circuit box. The sub-panel is connected by the hot lead and has it’s own ground including a second grounding rod. There is a home surge protector installed at the main circuit box.

I have passive conditioning on both lines for the components, yet I’m still hearing noise thru the speakers (from about two feet away). I live in a city and I suppose it could be dirty power from the grid.
Now to my question; is there a noise filter that can be installed at the site of the circuit panels? My electrician offered a surge protector with noise filtering (plus EMI/RFI), but was very expensive. So, is there a device that can be installed upstream to lower the noise floor?
Many thanks.
128x128lowrider57
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.
I have a BPT 2.5 Signature Series and my system is dead silent. I just checked U.S. Audio Mart. This is the unit I would have purchased had I been able to find one used. I get your funds situation but this is an excellent buy. http://www.usaudiomart.com/details/649370283-equitech-2rq-20amp-balanced-power-transformer/

Here is the Equi=Tech price list confirming the price of this unit...
http://www.equitech.com/purchase/retailprices.html