Strange noise is coming from psu

Hello guys,

I have just bought a new computer but I have already a problem. Before that here is my system:

Mainboard: P55-UD3R
CPU: i5 750
GPU: Ati HD5850
HDD: Seagate 500gb sata
RAM: Kingston 4gb HyperX 2000mhz dual channel
PSU: FSB Bluestorm 2 500W
And I am using Vista Home Premium

The only old element is my psu here which I have been using for a year. After my first boot with my new system yesterday I have realized something out of order. Just after the format thing I have heard a strange noise from my pc. It was something like: tısss tıs tıss... Anywa, first I thought it is coming from my harddisk. After the windows install, I shut down my pc and changed my harddisk with my older one. ( Samsung 160gb sata) And the noise was still there. When I closely listened I guess it was coming from psu. The other strange thing is, there isn't noise during system start. However, when the windows opens and I see my desktop, the noise is starting.
My first theory is: My PSU is not enough for my current hardware and the time my video card starts its real action, my psu is having a hard time.
Second theory is: my psu is somehow damaged.
Or there is something else going on.
I am looking forward to your ideas. Thank you.

the psu is crap

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Thank you for your answers. Before the final decision I want to tell you the tests I made today.
First I changed my graphic card with my older one. It is an ati x1800 xl. But the noise was still there. Then I put my new card back and changed my HDD this time with older one which is samsung 160gb sata. The noise was still there as well. As I mentioned before there is not any stange noise during system start but the second I see the vista logo and then my desktop, the noise comes.
Then I decided to test only my psu this time. I removed everything and installed my old pc. As mainbord asus p5b, 2 gb kingston ddr2 667, intel core 2 duo e6420, x1800xl + 160gb sata samsung. There wasn't any noise this time! It was just as I remembered. Stable and quiet. I even made a clear format-vista install.

Now here is my question: I am using my new board with 4-pin cpu power connector. But there are 8 slots there. I looked at the manual and some forums and the general idea is that as long as I do not make overclock it is ok using it like that. Is this stange noise related to my 4-pin issue? Have you heard anyhing about it or experienced?

Or is it all about having insufficient power supply? By the way I am also using a UPS which is 650VA and 1.5 years old.( It saved my pc countless times from the voltage changes in my neighbourhood.) Is it aslo a factor here?

Or as you said before my psu is damaged.

Thank you.