Help I think my AC is polluted

After months of trouble shooting, I've come to the conclusion that my AC is the culprit of a very annoying hum. 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.

Let me give a few details about my system.
- I recently installed two dedicated 20 amp lines. This did not change the intermittent hum.
- I've tried cheater plugs during the hum and they had no effect.
- I'm in the process of auditioning two power conditioners. The Equi=tech Son of Q Jr. and the Furutech e-PT609. Niether of them has had any effect on the hum when it's happening.

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. The hum doesn't change whether the powercords are plugged into the wall or either power conditioner.

I'm going to give the power company a call but I don't expect much help from them. I may try putting in an isolated ground and see if that helps. According to Equi=tech, balanced power should take care of most all ground loop issues, so I don't think an isolated ground will help much with this problem.

Has anyone else ever experienced this? Any ideas on a solution?