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drdna wrote:

It is not exactly correct. There is 60 Hz hum eliminated by lifting the ground to the amplifiers. The neutral is connected to the ground prong and chassis in the amps, so I assume it is setting up a loop. However, there is a second problem of higher frequency hum which is eliminated only when the PP2000 is unplugged from the wall and runs from the battery. I think my thought would be if there is some way to treat the AC power input to the PP2000 to eliminate the second hum.

The “higher frequency hum” is most likely the 120Hz hum or the hum that is coming from full wave rectifiers of your amp. It is not the problem of the PS itself but the PS in context of particular grounding schema. When a PP2000 is unplugged from the wall and runs from the battery it is not that PP2000 is unplugged but the ground via PP2000 is unplugged.  You most likely have no noise because you have another path to ground and your system is perfectly grounded. When you introduce the PP2000 you introduce juts another path to ground. I still do not feel that it is PP2000 related. You can very easy to measure if your PP2000 shorts the ground – it shell be 0R from PP2000 ground input to output.  Then you would need to find what create the loop. There are two ways to do it. First way is shorting the loops with a shorting cable that you need to bridge different ground points. With some proactive it could be very handy. The simpler way is to plug juts one amp one speaker and one souse into the same power stir (or PP2000), get no noise operation and them add one element per time and to see when the hum show up.

drdna wrote:

The sounds continue to change from day to day.

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