My Fatal1ty board has a USB Wake function. That combined with on/off charge meant the mouse stayed awake so any movement booted the pc. A fly had repeatedly landed on my mouse because of the red LED moving the mouse wheel which was set to "free-scroll" believe it or not. PC then booted. Solution was just to set it back to clicky-scroll (G500).
Anything on your PC that is still powered after shutdown?
Our portable HDD keeps spinning too! Maybe after serveral hours of inactivity it polls to the Pc causing a wake.
If they are wireless and have switches to turn them off rather than standby, turn them off![]()