Hey, So, are Hums from these Mac Pro's normal? I'm asking because I haven't been able to find a definitive consensus from the net. My Mac Pro, which I got used from an eBay reseller has a hum. I've since put books on top of the Mac Pro and that has somewhat mitigated the hum to a low and more tolerable level. It's not fan noise or HDD noise. I've since cleaned and dusted the Mac Pro. And, the hum is still there. Is this a defect, a dying component or is the HUM just a normal occurrence with Mac Pro's since they're all aluminum with little vibration reinforcements that they hum like this? Thanks! PS--the HUM sounds like a Yoga Instructor meditating and humming. It's a constant HUMMMMMMM... if you know what I mean.... PSS--My Mac Pro is 5,1, mid-2010, 6-core CPU, etc. The tower one.