Random Triangles on Display

It's probably the GPU. If it is an insignificant thing that happens very rarely, I wouldn't worry.

 

I had something like that happen to my iMac one and the graphic card was going bad

 

Looks like a failing GPU or artifacting.

Does it happen on a cold boot? Or only after the machine is hot?

If it's related to heat - you may be able to clean up the fan ports - increase fan speeds using SMC Fan control to keep temps down.

You might even want to consider applying fresh thermal paste to the GPU heatsink.

If it's happening at cold... ehhh, sounds about time to back everything up and look into a repair...

 

Did it happen before 10.6.8? If not, you could be lucky as it may just be a driver problem.

Otherwise, I think your graphics card is dying or it's a temperature-related problem (see Big-TDI-Guy's post).

 

Don't put it off, the longer it runs at higher temps - the more damage being done. The video card is not easily replaceable - even for those of us that have access to the equipment and parts.

Get iStat Menu and check your temps where the problem occurs.

I'd then open it up, remove the heatsink and cleaned the hell out of it and the GPU / CPU with Acetone to remove anything left behind. Get some decent heatsink compound, Arctic Silver or something thereabout. Apply it, don't use too much / too little, assemble and be sure to check that it's secure and flat.

Blow out any dust from the fans / fins with some compressed air, don't forget that tiny fan behind the stand piece.

Power it back up and check your temps, they *should be* lower now. As an added safety, fire up SMC Fan Control - and I'd increase your fan speeds (mainly the one feeding the CPU / GPU) by a couple hundred RPM. So things are still quiet enough to tolerate, but airflow is just a tad higher. I increased my main fan to about 1600rpm as a minimum speed, and so far things are kosher.

 

The ATI Radeon x1600 is a faulty chip. It's very similar to the problem Apple had a little while back with NVIDIA, the only difference being that while Apple acknowledged the NVIDIA problem and offered repair/replace/refunded repair costs on models with that chipset, those of us with the Radeon have basically been told go to eff ourselves. Also note that iMac users that had a Radeon x1900 installed (same family as the x1600 IIRC) were also given the same level of support as the NVIDIA 8600 users, but those that bought a machine with the 1600 are left out in the cold.

You can read about it here:
https://discussions.apple.com/thread/1697470?start=0&tstart=0
https://discussions.apple.com/thread/1732374?threadID=1732374&tstart=15
https://discussions.apple.com/thread/1726184?threadID=1726184&tstart=30

I was just at my nearest Apple store today dealing with this issue. They were incredibly condescending and basically told me I was out of luck and would I like to buy a new machine. You can find a documentation of my experience toward the end of the first linked thread.

Not that it's likely to help, but I emailed Steve, too. Better than nothing.

The graphics card is soldered onto the motherboard, so the only real option is to replace the motherboard. The problem lies in the fact that even if you did this, you'd be replacing a part that's dying for certain with a part that is practically guaranteed to die at a random point in the future. Could be 3 months, could be 4 years, with no real way to tell.