bad PS?

[Alejandro]

I've assembled my new system and it works great. Here are the specs:

Celeron 1.1 Ghz
128 MB RAM Kingston
Motherboard Soyo 7VBA133U
2 Maxtor HDs, 1 LiteOn CDROM 52x
AGP Geforce2 MX200 w/32 MB, Winmodem, ISA Network card
ATX case w/ 300 watts PS

However i have an issue: The power supply has it own power switch on it's back. When it's turned on (but the machine is off) a very acute sound is heard, so acute that it's not so easy to tell it comes indeed from the power supply. When the system is started, the sound is gone. When Windows XP shutdowns the system and turns it off automatically, it's there again. The only way to get it off is either turn off the PS switch or pull the plug.
I've tried turning the PS on without it being connected to the motherboard and the sound doesn't come up.
The hardware monitor tells me that the voltages are all correct with minimum variations.
Is this something to worry about?
thanks

[YODA74]

The ATX supply is designed to always deliver a voltage to the
motherboard, even when the computer is turned off. It is therefore
important to disconnect an ATX machine from the wall outlet whenever any
work is done inside the case to prevent damage to internal components.
I personally wouldn't worry about it you just have a noisy power supply.
But if it gets anoying you can turn it off.

and ATX is not like an AT it will not start without being connected to the MOBO.That is why it did not make a sound

[Alejandro]

Maybe it's just noise as you say, however i don't wanna take risks with my new machine, so i'll replace the PS.
The sound is very acute, but also loud enough to force me to turn off the PS, otherwise i would go mad!
To give you an idea, it's similar to the noise some old monitors begin to do after years of use (a constant noise that it's difficult to say where it comes from)

[YODA74]

If it's a new supply send it back and tell them that it makes noise. Could be the tranformer is not good Thats about all i can think of there isn't much that moves in one except the fan

[Alejandro]

Yeah i will. I don't like the idea of disassembling the entire machine in order to change the case with the PS, but i have no other option.
Thanks for the replies

[deddard]

A high pitch sound from a PSU could be due to a faulty Capacitor - best send it back for a replacement.

[mjc]

My thoughts, exactly send it back...

As has been mentioned, a faulty capcitor, transformer, or fan can cause noise.

Also don't rule out that a fan on the motherboard is still running, the only way to find out is to open it up.

[Alejandro]

sorry guys, forgot to finish this thread. I already replaced the PS but then realized it was a damn modem that did that noise when computer is off and PS on.