Are you using integrated graphics while mining? I get artifacts when I enable the display output on the 7970 while mining, that's pretty normal since you're using 99% of the GPU then asking it to also render the desktop.
Thank you for the help.
I'm using the 7970 to mine and display my desktop, so that makes sense. I have a feeling I get better Mhash/s when the monitor is off, because the fans on the GPU sound different as soon as I turn the monitor on.
The tasks I do on the computer usually don't require the help of the 7970 --- motherboard has onboard 256mb graphics --- is it possible to use the onboard graphics for my display while the 7970 is dedicated to mining?
Yeah there should be an option in your BIOS to default to integrated graphics, possibly in a "north bridge" section. It might also just work if you plug your monitor into your integrated graphics port. I default to PCIe and use a cable from each card into the DVI and HDMI on my monitor so I can still game if I feel like wasting mining time

The cables are also an easy replacement for dummy plugs if you have spares laying around. If you select the onboard graphics in the bios you might not be able to tweak some OC settings (I wasn't able to change voltage for example, although there might be some way to overcome this, flashing a BIOS with your tweaks would probably work, but that comes with its own risks and warranty issues). It might vary by motherboard too. When I boot I have all "monitors" on so afterburner can apply my OC, then I disconnect the display coming from the mining card in the windows screen resolution panel (where it says extend my desktop, etc.). That way the card isn't doing any extra work rendering an empty desktop. When you do that though you can't track temps or change the OC. There might be a way to overcome that too that I don't know of. I make things a little easier on myself by setting up profiles in ultramon (not freeware) so I can do it with 2 clicks. Sorry for the wall of text, but I'm a bit tired and just walked my mom through uninstalling/reinstalling IE over the phone. My mind is about as orderly as a bowl of noodles right now. I've been maxing out my OC so I'll probably post my final numbers tomorrow if it survives mining overnight. I was able to get it up to 740+ avg, but the OC was unstable with my temps well under control so I think I've found the ceiling for this particular card.