This is in reference to a Mac Pro 3,1 8-core purchased around Feb 2008. Lately, I've noticed a strange noise coming from my power supply that sounds like the noise a refrigerator radiator makes. It's a humming noise that rapidly comes and goes, constantly. The power supply fan speed was running at 599rpm yesterday, but is running at 629rpm today. I'm not sure if the problem could've been caused by adding additional ram (12GB, OWC) or an additional HDD (3rd HDD, WD), but I didn't really notice the noise until after adding these components. What could be the cause of this problem? What are my repair options if necessary (without Apple Care)? Thanks in advance.