Hello, the Cube is completely stock (except for the added RAM). Everything seems to be plugged in correctly.
The sound is some sort of a electrical "hiss". It sounds terrible, but as soon as the system idles it goes away. A part of me thinks that it's the HDD doing it, but im not sure that "hissing" is a sign of a bad HDD. Listening to it reveals nothing as it is very loud.
Do you have an ACD plugged into it? One of the acrylic ones?