Sounds like your fan. You know, that thing in your computer that spins and makes noise...
What did you expect? You didn't exactly give a lot of information. Just saying there's a noise coming from inside your laptop isn't enough to figure out what it is.
What does the noise sound like?
There are only 3 parts that SHOULD be making noise, no? Either the fan, the harddrive, or the optical drive.
Or it could be just your speakers being on. In fact, that's probably what it is.
Sounds like the fan to me. I honestly don't think its nothing to worry about. This is actually not as annoying as the sound the hard-drive makes.
I just think u are being a little paranoid.