Hmmm, it could be something daft like your AV software doing something in the background. There's no good reason for a FPS drop with an i5, so it had to be down to something running in the background.

Iv'e had this problem on my Hp laptop, try uninstalling a few games and re downloading toribash 4.5 it worked for me... Hope this helps...

Try lowering your graphics, I tried redownloading toribash it went a couple digits up but the real solution was deleting some programs.

I have 15 fps when i play with the minimum settings :> I have the best gaming laptop dont I? Call me crazy but I think toribash actually looks better with shaders off, so I suggest try that and get used to no shaders.

i use method b) form this
http://forum.toribash.com/showthread.php?t=363795
and its work. sometimes switching cores of CPU like gears in car

Sounds like a thing i had on my old laptop.

Your machine is just overheating and dropping power for very little time to cooldown.
After a moment it does it again and again. Dropping frames then good and then drop again.

Clean it.