I have a 2010 Mac Pro. It is on my desktop within an arms reach of me. My office is very silent. While I am working I can hear a "grinding" noise coming from within my Mac Pro. It is kind of hard to pinpoint where it is coming from, but I think it is the forward most fan near the front of the chassis near the USB and FireWire ports. To me it sounds like its a bearing problem on the fan. However, when I put my ear close the fan at the back of the chassis, the one on the very bottom, I hear a "grinding" noise as well. I ran a diagnostics check and everything with the system checks out fine. As you know the fan speeds in the Mac Pro vary by a few RPM. They are never constant (i.e. they may bounce around at idle from 600 to 597 to 608, etc.). And obviously they do the same when they are under load. So the strange thing is that this "grinding" noise is not always present. It seems like at a certain speed it appears and then maybe the fan changes a few RPM and the noise comes back. The problem is, its driving me crazy. Unless I play music, then it is a distraction. So based on my mechanical and electrical engineering education, I am almost, as I mentioned before, certain it is a bearing in the fan problem. So I take into the Apple store where it is nice and loud and tell the Genius what the problem is. I told him that he is not going to hear the noise in the store because of how loud it is. He proceeds to tell me that they want to keep it for 2 days to "stress" test it. I looked at him and said are you crazy? Anyways, I digress and that is beside the point. I have a better relationship with the business team at another Apple store so they told me to identify what fan it is, then get back with them and they will order the fan and have me bring the machine in and replace it on the spot. Now I said that is why I stay with Apple. So... Does anyone have any ideas? I downloaded smcFanControl, but I do not know what that Fan is called. Can someone tell me what fan is labeled what? I want to ramp up and down the fans to see if the noise is persistent at other speeds as well as try to pinpoint which one it is. Additional questions, can I run my Mac Pro with the side cover off? Can I take it off while the machine is on?