Help I think my AC is polluted

All transformers will hum to some extent, since they are being energized with AC. Audio tranformers are designed for 50/60 cycle operation and are designed and mounted to be as quiet as possible. One would expect those with iron cores mounted on a heavy chassis to be the quietest, as opposed to those without iron cores mounted on a light chassis.

The transformer/chassis combination is subject to resonance just like any material. If the external power is contaminated with large amounts of repetitive noise, one would expect the transformer noise to increase, especially if it gets near a resonant point. Also, sources of external AC noise can be very intermittant, such as air conditioners, industrial pumping, maintenance cleansing etc., which can explain your symptoms.

A really good solution to this is an isolation transformer on the AC mains ahead of the fuzes to the dedicated lines (e.g., a 4-5kva Topaz). The iso has the advantage of reducing common and transverse mode noise by up to 120db, eliminating any DC on the line, and blocking large voltage spikes. Some iso's also have additional taps to raise or lower the output voltage, if that is a problem in your area. Consider this approach as well as the power conditioners you are looking at.

Zargon - Thanks for the informative post. What is the cost of an isolation transformer such as the Topaz? How much work is it for an electrician to install? I had one hell of a time getting an electrician to do two dedicated lines. Would this be a better/more cost effective solution than a power regenerator?

I recently bought 2 - 4kva Topaz iso transformers at an industrial surplus supply for under $300 each. You can find them on the internet and ebay as well. It's best to get one locally, since they weigh in around 75-80 lbs. Topaz was a major supplier in the 60s-80s and many were installed during that period. These transformers are built like tanks and buying used should not be a problem.

You would need to pick a size that would accomodate your systems peak load plus a safety factor of 50-100% to avoid saturation of the core and distortion of the wave form.

The iso goes between the main panel supply and your dedicated lines. In effect, it creates a new source. If your dedicated lines are installed in the main panel, you would want your electrician to add a second small new panel to house those breakers. Installation is straightforward (hot, common and ground on both sides), however, he would need to ensure the proper wire sizes to code, and ensure the polarity of the lines are maintained across the iso (this is usually marked on the case).

You might have to search a bit for an electrician who has worked with iso's or is comfortable taking it on. Try a larger contractor that works on industrial sites or in hospitals or laboratories where iso's are common. Also, there are a number of us around that have done this and could provide additional assistance. Try looking in the archives as well.

Mootsdude posts;

The thing that's odd is it only occurs every couple weeks, and only for two or three days at a time. The other thing that's strange is it happens on the weekend and ends usually by Monday night.

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Is your house fed by a utility pole transformer?
If so go outside and see if you can count the number of houses that are fed from it. Sometimes 4 to 6 houses
Next thing to check is your neighbors that are connected to the same transformer. Any weekend body or machine shops. Any Arc Welding on weekends?

Next time it happens check the voltage at the power Amplifier's receptacle outlet with the Amp on and a source playing.

Take a walk outside and listen for any abnormal noises coming from any neighbors garage.
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I've put my ear right next to each component during the hum and found the Equi=tech transformer humming. I turned off all other components and the Equi=tech continued to hum, even in standby. When the hum is gone, the Equi=tech is dead quite.

Read the specs on the Equi=tech, bet it has a toroidal iso transformer in it. This louder hum than normal is caused by DC offset voltages on the utility AC line. Do a search on Google for more information, what causes a toroidal transformer to hum loudly.
I recently installed an iso xfmr for my Arcam Alpha 9 CDP. The Arcam has a toroidal power xfmr and at times the toroidal transformer was mechanically noisey. Connected to the iso it is quiet.

You also mentioned in your post that the lights in your home would get bright and dim. Brighter than normal? Do light bulbs burn out quicker than normal?
Jim

"Dirty AC" will not cause transformers to hum, but direct current in the AC line will (transformers are AC devices). It sounds like you're getting excessive DC in your house on those days. You can complain to the power company or you can buy DC blockers like the ones sold by PS Audio, Xantech, etc.