I am trying to remove a fan assembly from a MacPro 2009 (4,1) for cleaning. I believe this is the PCI fan. It's directly below the frontmost hard drive bay. I have loosed the screws and slid it away from a securing lip but something is holding it in place (something from the underside, where I can't see) What do I need to do in order to free the fan? I've googled but can't find a thing.