I have dedicated lines, but why is this happening?

One more question regarding Warrenh's post about a dedicated ground.

Sean, I searched your posts on isolated grounds here and I am still not sure I understand it.

When we installed my dedicated lines we used 12ga. Romex and 20 amp breakers. We ran each leg in conduit with the conduit tied to the breaker box, but with the conduit stopping short of the outlet boxes (plastic). The ground in the Romex is connected from the Acme outlets to the panel.

The only thing plugged into the outlets are my audio equipment since they are located under the house. I had a hole cut in the hardwood floor behind my equipment rack and ran all power cords out of sight through the floor to the outlets beneath.

How do I change this to make it an isolated ground?

An additional suggestion: try measuring the AC voltage at the receptacle before and during the moment the A/C system is energized. Buy a plug-in AC voltage meter from Radio Shack. At the instant the A/C system activates, the high starting current of the compressor may momentarily drop the AC voltage at your stereo to 100 VAC or even less. If your gear already draws significant current, or your entire neighborhood is blasting their A/C systems, or you have the whole house lit up, the voltage may already be dipped. If the additional voltage dip is low enough, one or all of the pieces in your system may be generating the pop noise.

Thanks for the suggestion, Bigdope. I will try it and see what kind of drop I get.

Bigdope, I measured the drop and the drop was 119.4 v to 118.8. Not much.

But it does seem this symptom started with the onset of much warmer weather when summer started. Things will begin to cool off on Maui by the end of the month. We'll see what happens as things get cooler into November and December.

Fiddler: Did you try cleaning the ground connections / ground rod yet ? I'm curious as to whether this did anything or not.

Other than that, it's possible that the fan motor has some type of capacitor or "condensor" that is going bad. These typically help to reduce or absorb the turn on "transient" or "spike" that motors or generators produce on start-up. Don't know if your system has one of these or not, but it might be worth checking into. Sean
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PS... Does this happen if you have everything disconnected from the amp with just the amp powered up and connected to the speakers ? You might try tracking down which component(s) it is coming in through.