TV turning OFF and back again ON randomly

TV model: Panasonic Viera TH-L32C8D

Type: LCD

Age: 11 years (bought in 2009)

Usage: Using it only with a set-top box

Problem

• TV randomly turn OFF and back ON again in a few seconds automatically. This happens randomly.
• There is a clicking sound when this happens. I think it is the relay sound.

Both, TV and set-top box are connected to separate wall sockets but there is a single switch to turn ON and OFF the supply to both wall sockets. The set-top box does not turn OFF when the TV turns OFF randomly.

It is not a remote issue, have checked it with both, the original remote and set-top box remote (I am using set-top box programmable remote to turn TV ON/OFF and control volume). Even while the remote is not in use, I have noticed this behavior.

What could be wrong with the TV?