Displays showing a yellow checkerboard pattern.

It's a Mid-2010 model, which I'm pretty sure is integrated graphics.

Like I said, we swapped out the RAM, with no change. That was my first suspicion.

Good idea on the temp monitoring. I'll look into that.

Thanks.

It's happening on two displays, attached to the two video ports. Both are DVI displays, but not identical. One is plugged into the mini-DVI port, the other to the HDMI port. The likelyhood of both displays being bad in exactly the same way seems remote, at best.

It's in an office environment. Lots of other cubes with standard office electronics.

But there's nothing of note particularly close to this setup. The computer sits on the desk between the displays, there's usually an iPhone and/or an iPad nearby. No printers, no scanners, and certainly no houshold appliances.

Perhaps we'll also try moving the computer to a slightly different location, although we've got other Mac Mini computers set up in exactly the same way as this one.

One additional data point. This problem did not manifest itself until after Lion was installed. I think we'll try the 10.7.4 update, and see if there's any change.