Game Slowdowns

In almost every game I play, I tend to get minor (10 fps max) slowdowns after about 10 mins of play. I've done almost every startup and registry hack i know to stop using memory, but I still get them. I've run housecall, adaware, spybot, kaspersky, and PCCillin, but no viruses have come up. I ran hijackthis and posted a log on the tomcoyote forums, but nothing came up. So, I have no clue what is causing the slowdowns, much less know if they are normal or not.

Are you overclocking? What type of system are you running? What game at what resolution are you talking about? The question is very general in its current format.