Loud Noises with my ps3

I was playing mlb 08 the show on my ps3, and all of a sudden, i hear loud noises, its happens wit any game because i played rbv2, and uncharted as well and still hear loud noises, i was just wonderin why is this happening, sounds like my ps3 is going to explode, do i need to buy a cooling fan for it?.:?

umm, is it almost like a crack? noise, a bit like pressing a keyboard jey a bit hard and fast?

I could just be the ps3 case expanding and contracting with heat?