Denman- Ask member Albertporter about preferential grounding schemes. Though they do involve adding at least one grounding rod, dedicated feeds from the main junction (not your audio system sub-box) box to the A/C and furnace and utilizing preferential grounding for your audio sub-box neutral and ground will likely eliminate the problem. Good luck.
Central AC Ruining MY System Sound
My system is connected on three dedicated lines.They are from a new breaker box fed from my original panel.It has five 20a breakers, three being used by the system,two left as spares.We had central air put in,which was installed when I wasn't present.They used the two spares doubled up.The net result,my sound is terrible.Images are shifted to one side,and sounds fuzzy.If I turn off the ac and furnace breakers,Everything sounds great.Is there a way to correct this.Can a separate line be brought in from the outside to a third panel box with just the ac on it.One electrician I spoke with says no.Also don't want and can't afford a power regenerating unit such as a PS/Monster etc.Would really like to hear from anyone who has had a similiar situation, and solved the problem.