Yes I think pmotz is correct about country testing.
Since this is not just in my home ,but also in dealer demo room .
First, I ordered P12 and delivered to my home, it has noise.
Then I go to dealer demo room in person, test it with his AC outlet and equipment, same noise. Then they offer a replacement.
Second day, new unit comes, I go to dealer shop again, and test the unit on site, however the noise is worse, as I said it didn’t even turn on any Zone yet. So it obviously need to replace another one.
The next day, I got call from dealer new unit is ready, I told them please test it by themselves first before deliver to me, make sure it’s silent. And they did , and soon the unit is in my home. I turn it on, silent, great! Then plug in my equipment, turn on zone, also silent.
I have been using it for 2days now, it runs silent so far, so I am happy with it.
So I am sure it has nothing to do with just my home AC quality, because the same issue happen in dealer shop.
In Hong Kong, the standard is 220V/50hz, Some place might have 230V variation. From P12, my home is 229.1V, and in dealer is about 228V. My THD input is only about 1.1%.
I wished this product works for any input as designed. So I didn’t expect to have noise, so do the dealer told me.
If this is not QC issue, may be we need another battery test in different country?