I have an Antec P150 and therefore a NEO430w powering the system as outlined below. The PSU is now sending out a high-pitched whine under load which seems to suggest there is a problem with it. I will take the PSU back and hopefully get a replacement in the next few days.

It has been suggested that the problem could have been caused by the PSU being underpowered for the rig. Out of interest I used the extreme power supply calculator at it came out saying that I need a PSU rated at 298w, hence 430w should be ok.

My question is this - is the PSU underpowered and therefore being pushed too much - hence I need to get a more highly rated PSU?

or

Is the PSU fine for this rig and I was just unlucky with the PSU unit that I got?

Q6600 (GO) - overclocked to 3.2Ghz @ 1.4v
P5K-E/Wi-fi
2 RAM sticks (1GB x 2) DDR2 800 RAM (1.95v)
Asus EN8600GT silent (passive - no fan)
Samsung HD501LJ SATA HD (500GB) x 1
Asus DVD RW
2 x 120cm fans (1600RPM - currently 1100RPM)
1 x 100cm fan (1500RPM - currently 1100RPM)
Antec spot fan (2200RPM currently 1300RPM)
scythe Karmameter fan controller
floppy drive with card reader
Antec P150 case

http://www.silentpcreview.com/article273-page5.html

Please see the warning addendum at the end of the review for this PSU.

"These are serious lapses in reliability, as far as we can tell, and the consumer's risk of being exposed to them by buying an Antec NeoHE power supply is still quite high. Even though our own experience with NeoHE samples is limited and not really that bad, based on the overwhelming user feedback on web forums, including SPCR's, we have to issue a warning that you buy an Antec NeoHE at your risk at this time. Until it's clear that the problematic early production batch(es?) are gone from retail stocks, it's probably wise to avoid the NeoHE, especially if you plan on using an Asus motherboard. It's really unfortunate, as a working NeoHE is likely the best quiet 80mm fan retail PSU available today. "

Note: I don't think it's underpowered.
Perhaps you could swap it for an EarthWatts 430w.
Then again, if you just do an even swap, you may get a decent one this time.

Just make sure you have your equipment evenly distributed between all 3 12v rails. Each rail only has access to 192 watts (with a maximum draw across all 3 rails of 384 watts), and if it's unevenly loaded that could cause some problems.

If you've got it balanced and are still having issues, then replace it.

Check your voltages in the Bios or with another program.
Check for dips in voltages.
If the voltage is off by more than 10% replace the PSU.