So, I bought my mac pro about 4-5 months ago and it ran great, except for a squeaking fan. I looked through the forums for advice and every thing was basically take it to the store and get it fixed. Flash forward to today. I just installed a new non-apple fan to the computer. So far its working, but I'm gonna see how it preforms. Regardless, I'm going to replace the one I just put in because it is loud as hell, but if one of your front fans has a problem it does seem that you can replace the fan successfully. To any one considering this I impart my knowledge on the subject. You need a 120mm fan, with a Four pin connecter. Not the standard one you would see in a PC, the kind that connect to directly to the power source. I had a three pin connecter, but it worked with one pin hanging outside the connecter. My fan that was dysfunctional was my front bottom fan. I've hear that changing the rear fan requires compleat case disassembly, so to any one out that that has problems with that fan I can't help you. Well, thats all I have to say so far. If any thing changes ill post an update, I'm going install the fan controls now (SMC I think it is?) good luck to you all with similar problems.