Problem with PS2

[laul]

Hello,

I ve got a PS2 v3 or v4 (i don't remember) with a messiah 1.
Since a few days i ve got a strange problem,
after a while (which may be only a few minutes) some part of
the image become blurred (like if there is noise) or strange display
appears as if it was interference.
It's not the laser, it read with no problem and even the main
menu (with the logo) suffer from this problem.
So if anybody has an idea i'd appreciate.

Thanks.