If your system is making a VERY LOUD (you can hear it in another room loud) geary/whirry sound (VERY distinct sounding like that alright), then THAT is a bad sound. It means your system wants to overheat. Shut it off immediately and leave it for at least an hour (take the game out just in case as well alright). Note that playing DVD ROMs and CD ROMs will increase your system's chances of overheating. So avoid them completely. Play ONLY Blu ray on the PS3 and your good.
Mine came close to overheating once. I've had it for 3 years, beat the crap outta the poor thing (not literally lol. I just play it for MANY hours at a time) After that I got the vertical stand for it (I have the Slim) and since then no problems. The reason it came close was because I played it for several hours straight, decided to play a DVD ROM on it without giving it a break, and it was horizontal near things. That would explain exactly why mine wanted to. DVD ROMs make the system work harder to play it. The laser moves faster and it spins the disc faster. It spins Blu ray at a much slower speed. So when you combine 3 things like that your asking for it.
Clean out the dust from the cooling system as well. The front, sides and back. Use a vacuum. DO NOT use compressed air because that COULD damage the system. Vacuums are safe though, don't worry. I contacted Sony just to make sure it was actually. I vacuumed my system the other day. Make sure you unplug it completely (take the disc out as well if it has one in it) and handle it carefully and vacuum it. You can use a handheld or a full size with a smaller head/bit to vacuum the system.
Get on the playstation website and look up FAQ, or go to a nearby gamestop with this question, if you have a warranty you can send it to playstation and they'll fix it for free, but you have look around on the playstation website
