I immediately turned off the computer. Later on I switched it back on and the noise was gone, however it returned after an uptime of 19 hours!
When the noise came up again I went looking for all movable parts inside the computer. I removed the power supply of the following components one after another (and put it back on) to hear if it would stop the noise: HDD 1, HDD 2, ODD, CPU fan. I even stuck a pencil in the fan of the power supply unit in order to see if it was causing the noise. I had no luck, I could not stop the noise.
Has anyone a clue what could possibly cause the noise? Can it be a pc speaker malfunction!? Or might it be something inside the power supply unit?
Thanks for your answer!
Unfortunately I can't fix the link in my first post.
You can download the sound file here: http://uploaded.to/file/e8jgpb5d (182 KB)
It would help me a lot if you could give me your opinion on that noise recording.
Looking at your picture, you do not have a lot of "movable" parts in there, basically just the power supply fan and your CPU fan.
When you stopped the power supply fan with the pencil the noise was still there?
If so it is not the power supply, unless it has another fan on the back. If so try to stop that, too. Also do this with the CPU fan (doesn't hurt the CPU if you just stop the fan for a moment).
Preferably use your finger on the middle of the fan and avoid using the pencil since this can "break/scratch" the fan blades which in turn can lead to noise.
If none of the fans is the issue, it can only be one of the HDDs, even though that seems unlikely, since that HDD shouldn't even work anymore.
foobot, I just found this conversation because I'm pulling all my hairs trying to find the source of a strange noise in my old Dell 3000. I went through the same steps as you and am also baffled. Did you solve your problem? Would you mind uploading the sound file in another way, because the current host won't allow me to download it in my country (USA). Thank you!