what is this Weird noises???????

[LoTeX]

I thought perhaps the monitor is made with bad quality plastic so the variation of the temperature made the plastic expand but the temperature of the room always is stable so must be something else.
Any one has any idea why this happen?

Mine does this after the computer is switched off (if it's been on for hours, like usually). It "tacks" for maybe about an hour (5-10 min cycle) and quite loudly, I actually close my bedroom door in order to sleep well. But other times it stays silent.