Sometimes while loading something or “working”, I hear a loud scratching noise from the computer that last a second or two. It’s not frequent, but it kinda freaks me out when it does it. The computer is three and half years-old. Should I be concerned?
Chances are this is your hard-drive and its not something to really worry about too much. After many years of use with lots of data written to a drive they can get noisy especially if they are searching around for data a lot.
The other thing is could be is a fan, if its a fan that doesn't turn on very often due to your case being well constructed then it could just be a wire that is in laying on top of the fan. just pop open your case and look around.
its your hard-drive if your doing something read/write intensive, like working on a file, saving or loading a big image/document and you hear the noise.
depending on the operating system winxp and lower (not windows 7 or higher) you might want to run defrag to put your files in order. If your worried about your drive you can also run Spinrite which is a useful program for making sure your hard-drive stays alive for years to come :).
other than that, maybe mice? :D
if it's software e.g. windows, then it could be this http://superuser.com/questions/333880/what-is-the-source-of-this-funny-scratching-card-shuffling-noise-in-windows
In which case, it's the dog in the windows xp search. You hear it more if you have opened many searches which can happen accidentally too. After some time the dog scratches himself and it makes a noise like scratching or shuffling cards.
if it is not from a speaker of any kind, but it is coming from the computer box, then open it up and listen for it and try to find it. Have the box near you when it happens. Fans are a moving part..see that nothing is knocking any.
Hard drives don't make a scratching sound but they can click.. it's worth using software like speedfan and checking the SMART data on the hard drive.
You need to do some troubleshooting to isolate where the sound is coming from. Time how long between one sound and another. If you get to a point where you can predict it then that will help you to isolate the place it is coming from.
A) A list of different computer's noise sources:
B) Noises from the Hard Disk (with recordings)
If the sounds comes from the hard disk it's unfortunatelly a bad news...
First check the S.M.A.R.T. data too see if the HD is really in bad condition. If so backup your data and change the hard disk before it's too late.
Free S.M.A.R.T. utilities are available with Piriform Defraggler or as an online utility within SpeedFan.
I suggest you to read the article on the SpeedFan site about «What is S.M.A.R.T. and how can we use it to avoid data disaster?»
Hope this help (and the sounds are not from the HD!). :)