High Pitched Noise from PC

I've started to hear a high pitched noise from my PC today, I'm not sure what it is. I am thinking it might be the power supply, which I could try replacing with one from my old PC.

The computer is about 3/4 years old, the only parts new to it are a Hard Drive (about a month old) and a DVD/RW (about 2 weeks old). Nothing else is new and from what I've read, if it was the hard drive, it would be constant and the driver wouldn't last much longer.

The high pitch noise only lasts till I reach the windows log in screen, then it goes away.

This morning, when I first heard it, I thought a cable might be loose, so I opened the case and made sure they where all secure. Turned the computer back on and there was no high pitched sound, yet I turned the PC off to leave for somewhere, come back and heard the high pitch sound again when I turned the PC on.

So I'm not sure what it is, probably need a new PC anyway, haha.

 

Open the case, leave the side off, grab an empty roll from paper towels and turn on the computer. If you hear the sound, hold the tube to your ear and move it around the components so you can try and determie where the sound is coming from. It could be a fan bearing.

 

I will probably have to try this tommorow, the thing is when it's already been on, if you turn it off and back on, there is no noise. Unless you leave it turned off for a few hours which I could try and if it works, modify this post.

I do wonder though, does a cold room affect any of the parts?