One of the front fans on my early '08 Mac Pro sounds like it's grinding. When I first boot up the fans are whisper quiet as they should be, but give it a few minutes and there is a distinct grinding sound and I've narrowed it to the top fan on the front of the case. When the system is turned of, the fan whines to a stop. Is there any way to lubricate the fan to solve this? The access doesn't seem very easy, and I'd rather not have to mess with the case assembly. Or do I have to pay some kid at the apple store a hundred or so to do it?