Annoying problem

Hello, I just received a second PS3 Slim that have the exact same annoying behavior than my first one.

To make it simple, they both make the screen to go blank for 2-3 seconds maybe once an hour, this is happening whatever the PS3 is doing (playing a game or a blu-ray, simply being in the XMB or listening to music, etc.) there are also some green glitches in the screen at the very moment the screen goes blank as when a graphic card is rebooting on a PC or something like that…

Does anybody ever notice that kind of thing?

And know why this is happening and/or know a way to fix it?

Any help would be appreciated :)

Additional note:
- Firmware 3.01

- Using HDMI -> 1080p

- Optical cable for sound
- Sound output 48kHz (because of the “no xmb while playing music” problem when using 44.1kHz)
- BraviaSync activated (the PS3 is linked to a Bravia 40W3000)
- There are a few PC on the same wireless network

If there is anything else you would like to know to help you to determine what the problem could be, just ask ;)