mw059 switching itself on

I have a mw059au that goes through the powering up sequence just like when you switch it on at the powerpoint every 45 minutes or so by itself, ie. all the lights come on and go out in sequence and you hear the welcome beeps. There also seems to be a small constant hum coming from the bottom area of the machine that I never noticed before and when I flick the power off at the wall I can hear a faint knocking sound from the same area.
I ran through the diagnostics test several times but never received any error codes to report.
Any ideas out there??