Dell :: Xps 1530 Counter Strike Source (css) Fps Drop Every 4 Minutes

I've noticed lately that my framerate will suddenly go from ~100 fps (I set max there) or so to 20fps.

It will do that for almost a minute, and then suddenly for no good reason shoot back up to 100. Also, there would be times when absolutely nothing is happening in games, and it happens.

I used to think the drop was heavy firefights or traditional graphic issues like smoke or textures, but when i turned everything to the lowest, I still observed the exact same trend!

Windows Defender reports nothing and Spybot Search and Destroy reports nothing. I went through NHC to make sure HD is set on max performance and also set Battery Usage on max performance. I *thought* that would help, but the same thing started happening again after a small period (8-10 minutes) of no slow down.

Current theories are:
1. The cpu is overheating so it underclocks for a minute or so.
2. There is some process that I can't find (I might have missed something obvious) that checks in every 4-5 minutes