I started looking into my hum issues and have noticed a couple things that I'll post here in case they help others.

1. I started cleaning off my workbench so I could open up the amp and noticed something was making the same sounding buzz as my amp. turned out to be one of the compact flourescent lights in my shop. Turning off all CFLs in the house didn't make a difference so I started thinking there's noise on my power lines.

2. I built an RF sniffer probe and started poking around my system to see if there was any radiated noise.
Power lines : Nothing
975: Nothing
Amp: BUZZZZZZZ
I looked at the amp and the noise peaks out when the probe is by the transformer.

Conclusions: None. But either there's noise coming in through my power lines. (This is called conducted noise.) Or something is going on in the amp that is generation the noise. I need to do more exploring. I'm going to try a filter on the power input and see if that helps.

Here's how I made my test probe:

I took an old RCA cable and cut the connector off one end. I then stripped off about 5 inches of the outer insulation to expose the shield. I twisted the shield up and cut it to about 3/4". I then stipped about 3/4" of insulation off the center conductor. Loop the end you just stripped around and twist it with the shield. A little solder and a little tape and you have test probe with an RCA connector on the end. Make the opening created by the center conductor loop into roughly a circle.

To use it I disconnected the RCA connector comming from the 975 and plugged the probe into the RCA input of the amp. Use the probe like a butterfly net (only slower). The opening of the loop needs to face the direction you are measuring. I had the kid listen to the speakers as I move the probe around. She would let me know when the noise got louder or quieter.