Power problems.... Ground, dedicated lines, ect

I called the engineer at Furman and he said I had a ground loop problem. He suggested I call a local TV or Radio station and find out what electrical company they used. Sure enough they ( local TV station electrical contractor) had a mans name who was the "ground loop expert ) The Furman engineer told me that "power problems" for audio/ video broadcast is more schooled on power issues. ( made sense to me ) I will post the findings and or solution when I get the work done.

Ground conduction can be tested with a 'megger'. ask around until you find an electrician that has one and knows how to use it.
I, too, have a 100amp panel and a 20amp line to over 1kw of amplifier. No Problem!
In the old days, my Carver Cube could make the house lights flicker in time to the music! Now, I can turn it up to nose bleed levels without a flicker. And, with the A/C on.

For example, the lights dim when the air conditioner comes on.

That is quite normal. As you draw more current the voltage tends to drop - often the current draw when an AC starts up is very high - your lights should not remain dim but the slightest flicker is not at all uncommon.

First and easiest approach is to make sure everything is in the correct phase.. This means your Neutral is actually connected to the neutral spade etc... on the outlet not the Hot... They sell "3 Prong" power testers that you pick up at the hardware store for between 8 and 10 bucks, they have 3 led lights on them, each light indicates a different issue with a legend key to tell you what it means right on the unit.. Basically you can not hook this tester up wrong, or do any damage, it plugs into a 3 prong outlet and automatically knows if you are missing a ground somewhere in the system, or have a reverse polarity etc..

You will want to go and plug it into each and every outlet you have hooked to your system, If one outlet has an out of phase connection and its just your CD player for example running off it, than its not in phase with the rest of the stuff plug into the other outlets, this can make a very thin and less dynamic sound for sure..

Problem is with A/C power units will still power up if phase is wrong normally, but if you ever look at an outlet you know one SPADE is a little Larger than the other and you take Power connectors on your cable and see that one SPADE is KEYED larger than the other as well so you can only plug it in one way... However that does not mean that the Wire in your wall is not hooked to the back of the outlet in reverse because they all fit anyway you want!

This could cause you to have more noise and dim lights too from what I understand if you have your refridgertor or washing machine etc... Plugged in out of phase as well because the outlet is installed backwards on that unit, and it goes all the way back to your panel so it can effect other things upstream...

Best thing would be go and plug this device into all the outlets in your home and check the phase on everything and correct any that are wrong.. Obviously this would not effect the performance of your microwave or alarm clock but could cause Video and audio issues I guess..

I have no clue if this will help, but I have done this in the past and had better results. here is a link to the type of tester

Oh and I am sorry wrong terminology I did not mean phase exactly but POLARITY Testing all your outlets see link

http://www.mcmconnect.com/tenma/product/72-6791/Miscellaneous%20Testers%20and%20Meters

I'd like to hear the explanation for a ground loop causing your lights to dim when your ac powers up. Ground loops cause 60 Hz hum due to unintended potentials introduced into the signal path - not your light to flicker when your ac kicks in. Sounds to me like an answer from a telephone jockey with a cheat sheet sitting in front of him or a "techno term of the day" answer. Given the source - tanatamount to "its not the fault of our equipment."