Right now I'm just basking in the glory of having found the root cause of most of that noise on the lines, and started looking for a source of affordable "good" 9V 5A power adapters.
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not trying to 'rain on your parade'..... it is possible that isn't where your noise is coming from...... if you haven't already, put a 10 or 100 microfarad electrolytical and a couple of .1 or .01 microfarad caps at the output of the power supply..... and I didn't look to see but you would want to put the same capacitor duo on each separate circuit board..... that SHOULD squash the noise. Plus..... a bunch of interconnected grounds running here and there are often culprits for noise. And keep in mind that often serious engineers and engineering is involved with noise and interference