Re: XPS 430 PSU Fan & Speed issue
Check the actual power supply when the fan speeds up, the fan in the power supply is reacting to the heat in the power supply not the overall heat in the PC. However, when you open the case it allows more air in and with more air the power supply is probably cooling down. I would check to make sure there are no obstructions to the cooling fan or power supply air intake.
One comment, the fan on the Dell OEM power supply in my Dimension E510 desktop was always noisier than I thought it should be. OEM power supplies are not the "best" around and same way with the fans. I did some hardware upgrades to my E510 that also required more power than the stock power supply could handle and I replaced it with an Antec Tru Power Trio 550 watt model and the fan in it is very quiet, even with a load on the power supply (there are many good brands out there, this particular power supply just happened to be on sale at CompUSA when I was looking).
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