Really Odd Graphical Glitch

[Tech-Minded]

I'm running a 2007 20 inch iMac with a 2ghz intel core 2 duo. This Problem occured while on southparkstudios.com right when I hit the mute button on my keyboard. Not looking for any troubleshooting because it hasn't happened since, just thought I'd share the abnormality.

 

[TMRaven]

Is that your hard drive making that knocking sound?

 

[Tech-Minded]

Probably, but its SMART status is verified.