Macbook Pro 12 making loud "brrrrbrrrrr" noise.

Hi
Recently my Macbook Pro '12 has been extremly slow and not responding. Im having to restart it almost twice a day! the other day when I restarted it something really weird happened. My Macbook was making this really loud "brrrrrbrrrr brrrrrr!" noise. This continued for at least an hour until it died out and was replaced by the fan getting extremly hot/loud causing my Macbook to slow down again and lag.

It has been okay since but still very slow and having to restart at least twice a day. A few hours ago my fan started heating up for no apparent reason and the same "brrrbrrr" noise was there faintly in the background but slightly different, instead of ontineous it was: "brrrbrrr. *pause* brrr!". I have made an apple appointment but would also like to hear what you guys think it could be?

Here is a video of it (turn volume up)