LCD making noise

Hello there,

I got a Sony SDM-S53 LCD monitor, it works quite well in my opinion, but there's one thing that bothers me : it makes a tick noise (like a clock) once in minute or so even when turned off! I even unplugged it grom cables and it continued to do so and stopped only 15 minutes later (there's a tick sound roughly one in 30 seconds)

Is it a common issue with LCD or mine's a faulty one?

thanks,
Udi