My MacBook Air keeps on hissing?

Whenever I watch Netflix or whenever my brother plays Minecraft, it starts hissing after 30 minutes or so. The hissing is coming from the left side of the Mac, where the charger hole is. Whenever it hisses, I close the laptop and wait until it stops hissing. When I reopen it and start using it again, it hisses again. Can somebody explain why my laptop is hissing and how to prevent it?

Hmm i'm a windows person but i may know the problem. Have you been playing it on soft surfaces or hard such as wood. If so then lint could have gotten in it and you have to get it out by taking it to the computer store.