Brief graphic glitch right before screensaver

I have a 2013 iMac running OS 10.8.5. Lately I've noticed that, whenever I manually initiate the screensaver (one of the included ones, "Shell"), there is a momentary graphical glitch before the screen saver begins. This happens when I both move the mouse cursor into the hot corner and when I preview the screen saver within the system settings. My question is: is this cause for alarm; is it heralding an imminent logic board issue?