Experience emilinating Ground Noise?

I need help gettig rid of the various noises that plague my McIntosh system through my loadspeakers; I have an MX130 pre-amp, and MC206 6 channel power amp, a McIntosh CD player, as well as a Panasonic DVD player recorder, and a cable box processor. I purchased a Monster HTS 5100 which did not get rid of the various buzzes that come through my speakers, but I did learn that when my voltage exceeds 120 the noises start. When it hits 125 volts it sounds like I'm being attacked by a plague of locusts, it's very noisy. Initially I had some luck getting rid of noise by eliminating the ground phugs, but this was only a temporary fix. Would love to hear from anyone with experence solving this sort of issue.
various companies make a device for cable boxes, this is most times the biggest culprit. To test this just remove the cable to see if most or all of the buzz flys away.
A couple of fairly cheap ways to lower the voltage.
Check out this on ebay,

Another way is with a buck/boost transformer wired in a buck configuration.

What is the voltage rating of the audio equipment, 110V, 115V?
I assume when you are taking the voltage readings you are taking the reading with the load connected, the equipment turned on.
What time of the day is the voltage 120V? What time of the day is it 125V?
The next time the voltages is 125 volts take a line to line voltage reading. See if it is 250 volts. Is it less than 250V? How much less?

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Worked for me.
Buy a battery powered amplifier. LOL
Sorry I couldn't resist.:-)