2 hours is the exact same time that its set to go into standby after inactivity
to be sure this is the culprit, can you try changing that setting to for example 30 minutes, and see if your PC now wakes up after 30 minutes.
I had a similar problem under windows. it was set to hibernate after a certain time, and it would wake up from suspend mode to hibernate. Not great when this happens in the middle of the night!!!
I also had another problem under windows, it would wake up at 3am to do software updates.
Anyway, let us know if changing that 2 hour setting changes something so that we know this is where we should focus.