I'd recommend taking the cover off, clean out the inside with some compressed air, then reconnect the computer and power it up and see if you can identify the source of the sound. The compressed air will help blow all the "gunk" and "dust bunnies" out from inside. If you ID the problem, and it's a fan, then you can usually replace the fan, but it's dependent on how much of a "whine" you're talking about. Most computer fans will start making a little noise after they get some age, so it's not necessarily an issue unless it's quite loud or the computer is starting to reboot on its own, etc. As a precaution, always make good and current backups of your important documents.
And remember, if you need some help, there are usually quite a few good local shops around.
Hope this helps.
Gateway 500 series, a little over a yr old. Windows XP. Recently begun to get a high pitched whining sound coming from inside the computer itself. I think its either from the HD or a fan but not sure. Too scared to open it up as I'm a relative newbie. NOT affecting performance at all but extremely annoying and also worried it is a sign that some part is going bad. Anyone w/ experience have any idea what the noise could be? Thanx.