IMac :: Computer Making Loud Constant Noise / Sound Coming After 30 Seconds

My family just recently upgraded from an old PC to this 27" iMac, during the early part of the summer. While using it over the last little while, I would notice a noise that sounded like a harddrive spinning or possibly some sort of a fan noise. The best way to describe it would probably be as digital noise. It's not incredibly loud, but it's a decent volume, and can get quite annoying. It has a little bit of a squeak to it.

Over the last little while, it's become more constant. When the computer is in use, it'll usually occur quite often. It's quite annoying and obtrusive when I'm watching videos and I'd like to know what it could be.I think our computer is still under warranty, so I'm hoping to find out if it is something wrong, so I can get it replaced.

I've also been wondering if it's a fan, or a regular noise. However, it's so constant that I'm starting to wonder. The other night, I was watching a video and it seemed like it was coming on every 30 seconds for a long span of time. We don't run any memory heavy programs on this computer. If anything, we're just using Firefox, iTunes and/or Messenger. Sometimes Office. There's little to nothing stored on this computer, as it's brand new, so most of its memory is free.