My MacBook Pro is making a weird noise...

When i run a game on my Macbook Pro or even like tonight I was running videos and it sounds like a knocking noise or something near my HD or fans. I am hoping it is nothing major, It ONLY does it when I run a game mainly. Never really happens when i stream videos. except for this once. Does anyone know? Or can anyone please help me out? I just got it about a year ago this month. So I hope its not already messed up. I take care of my computer..I dont have the money to replace it either..

Thanks guys,
Michael

Sorry about this post guys. I noticed as soon as I posted it I posted it in the wrong section. I meant to put it in the notebooks section but completely clicked the wrong one. So Sorry ahead of time. lol