I got a coolermaster power supply off newegg, since it is better then my old powmax, and it doesn't sound like a jet engine. First time I plugged it in, the fan made a metallic ping sound at a rate of about 0.5 per second. It gets quieter and quieter, and then stops once the computer finishes booting and windows begins loading. Looking at the fan-speed vs load chart that the PSU came with, it seems that when the fan is spinning slowly, it hits a component inside the PSU. It only makes this sound when starting it cold, after it hasn't been running for at least 10hrs. Should I RMA the PSU, or just use it anyway?

I've had powersupplies that did that in the past, it's never caused me any problems power wise, and they lasted about the same length as a powersupply does.

Well, I'd RMA it, personally. If the next one you get does the same, you know that its okay, and that they "all do that sir."

If it doesn't consider yourself lucky.