I have a client whom has a 20" iMac running 10.6.8 with 2.16 C2D CPU. The problem they've been experiencing is sometimes there will be a diagonal line in the screen that just appears and it will not go away until the system is restarted. When playing Hulu and other video the video will sometimes freeze and the sound will continue. Shortly there after the sound stops and the entire machines freezes. Only way to correct this is to hold the power button down and then turn it back on.
I've had the machine for a day now and have not been able to recreate these issues. I've tested it with the Mac diagnostic mode by holding the D key while booting. The short and extended test finish with no issues.
I have a hunch these issues are related to the video card but I don't know how to stress the card in a Mac. First thing I've done is remove all dust from the machine. Thanks in advance.