It would be your power supply when you leave it on standby any flutuation in the electricity will caus it or any other device on standby to auto start like a television etc and that would be all it is most likely unless you have it set up to wake itself with phone lan etc but I guess a very slight flicker in your power could be the culpurit which could mean there is a bad connector on the transformer near your house or even a bit furthur away this also means you will most likely be experience a power outage soon.