Yes, it does this with all files including the stock ones. Yes, the parameter I edited in the the config editor, I think it's called Humstrt, but again that only affects the power on. I have always formatted the SD, although not with a "SD formatter" is that a program made for nec?
After watching some videos showcasing NEC boards, I'm wondering if they are even set up to mix the poweroff sound, because it doesn't sound like there is a background hum in any videos on power off. Perhaps I am wrong?
Do you have an I2 to compare with?