Electrical issue

I have an electrical issue/s that I could use some help with. It's a hum issue, but after exhaustive research here and on AA I still cannot figure it out. I have 4 dedicated lines for my stereo run approximately 75 feet with 10/2 romex all connected to Porter Ports. I own Von Schweikert DB-99's, which have a powered sub built in. I have tried lifting the grounds on all the equipment except one(and every conceivable variation,I think), I've tried plugging everything into a power strip and then that into just one outlet, I've even tried using other outlets(not dedicated). In the end, if I disconnect everything and just plug the speaker into the wall with no other connections I will get a hum thru the woofer only. I have even put a PS Audio P500 between the speaker and the outlet to see if it made any difference to the hum, but no luck. If I leave the speaker wires connected and turn on the main amp then I will hear hum thru all the speakers(tweeter/mid/woofer).

I called VS and spoke with Kevin and he said that the signal is split in the speaker before the sub amp which would suggest that the hum is coming from my electrical system rather than my equipment. IOW, if I heard hum only thru the woofer and not the other drivers when the main amp is connected then there could be a problem with the sub amp, but this is not the case.

My house is new and the electrical and grounding system seem to be in good shape. I have checked every outlet I could find with a polarity/ground checker and did not find any problems. My panel is grounded both to the water line and a spiral rod buried next to the house. According to the builder these are acceptable to code here in Austin, Tx.

The only thing that seems odd is that when my A/C turns on, and sometimes my TV, the lights will dim for a second. I had the builder double check all the connections and made sure the proper gauge of wire etc. was used to hook up the A/C, but nothing seems to be wrong. Is it perhaps the Transformer on the pole outside? It's definitely old as it looks a bit rusty up there(new house - old neighborhood).

The hum is not particularily loud, but i can here from my listening position 10 feet away when no music is playing. I appreciate any help you may have to offer, and I'll answer as many questions as you have because I'd really like to solve this.

No, I did not get that done. The city however has told me they will not do anything about the hum problem as I do not have a voltage problem as far as they're concerned. I thought the iso tranny would help kill any noise coming from the main transformer? Any ideas?
I guess I could use some help clearing my head:-). What should I do next? The iso tranny didn't work, the electric company seems to think there is nothing wrong with the transformer, no amount of Quietlines or Enacom filters seem to have any effect. How do I stop this hum??? It's driving me freakin' nuts. The electrician will not hook up an outlet in the manner Nerspellsner describes because he says it would be against the law, a felony I believe. Granted it would only be for a few minutes but he's not going to do it. I really don't know what else to do. Any help to offer?
You dont have to (steal) power to do this test. I will describe the legal way to test your power. This has to be done by a licenced electrician. Open your meter socket.Leave the meter in the socket and disconnect the feeder wires at the load side of the meter socket.As long as the meter is in place, you are not stealing power. Connect a fused or circuit breaker protected outlet attached to an extension cord long enough to reach your equipment. You have to find out if the hum is from the street or is coming from your house somewhere before you try to fix it.
A few more questions. Do you have only one main electrical panel or do you also have a sub panel installed. Is your main circuit breaker in the panel or in the meter socket? On to another subject. There is a chance that somewhere in the house, a bare ground wire is touching the neutral terminal of an outlet. This problem would not be indicated with a plug in outlet tester. If the ground touches the neutral, current will be flowing through the ground wire and produce a hum. I hate to say this but the only way to find out is to remove every outlet in the house and visually inspect each one. Sometimes you can see the problem by just removing the cover plate. Turn off the circuit breakers before you do this. You can wrap the outlets with high grade electrical tape to cover the screw terminals to prevent the ground from touching the neutral screw. This problem could also happen in light fixtures or switches or even a screw or nail going through the cable but much less common than the outlets. Before spending time doing this, find out if the hum is originating from the street or your house by using the method described in my previous post. Good Luck.
Thanks Nerspellsner! I didn't understand clearly before what you meant. I will ask my electrician about it and hopefully get him to come out and give it a try.