Memory and cpu usage look fine. The cpu is hardly used at 26% and memory is only half used. Cpu usage should go up during gaming as well as gpu usage. It could be your cpu fan, but chances are it's your gpu fan spinning up while gaming that gets louder, that's common. My hd 7850 is whisper quiet until I load up far cry 3 or something then it sounds like a small vacuum cleaner.
Have you made sure steam is up to date, all game files/patches are up to date? Sometimes patches improve fps other times they hurt them in cs go. Many people have had issues with this. When you snapped that screen shot of your system, was it at idle? (not downloading anything, not running any programs etc). 26% would be a bit high for idle though it does appear to be spiking (which is normal) and not a steady 26% usage.
Granted this is 5mo ago, but sounds similar.
https://www.reddit.com/r/GlobalOffensive/comments/2vqbdo/huge_fps_drop_since_update/
Just looking through some threads about this, this seems to be par for the course with cs go. Regular update hell for people (I had to research a bit, I don't play cs go). You could try a virus scan, malware scan with something like malware bytes anti malware (mbam), another person passed all these things 'clean' then ran this anti rootkit and found something that others had missed. It helped their fps.
http://support.kaspersky.com/viruses/disinfection/5350#block2
Edit: here's a csgo 2015 tweak guide that may or may not help improve your performance.
http://steamcommunity.com/sharedfiles/filedetails/?id=225142771