what is the cause and how can I rectify?

My Panasonic Viera TX-42G20BA sometimes switches itself off and back on again. This does not happen often but generally soon after switching on. Any idea possibly of the cause and what needs to be done to rectify. When this happens the green light stays on and a clicking sound can be heard from inside the set possibly coming from the power supply board. Also the same clicking sound can be heard occasipnally when the set is in standby mode.