I just had this problem! My laptop would run games perfect, but every 15-30 seconds I would get a drop to about 7 fps for a few seconds. I came here and was given the idea that my video card may be overheating and fans needed cleaning. I was reluctant to open my laptop so i blew into the vents fairly hard and a TON of dust flew out.

It fixed my problem, but it seems like your drop in fps is a little more spread out.. Hope this helps you out a little!