When I originally got my MacBook Pro, it had an issue with high-pitched processor beeping. It isn't loud, but it is annoying in a quiet room. You can tell that it's coming from the processor, right above the keyboard where it's really hot to the touch. I installed the Processor preference pane from the Developer Tools, and the beeping went away if I turned off CPU2. If I turned CPU2 back on, the beeping came back. I could also get rid of the beeping by running Photo Booth. The MacBook Pro originally came with an earlier version of Tiger installed. Eventually, however, the processor beeping seemed to stop. As of a few weeks ago, when I had Mac OS X 10.4.11 and all the latest software updates installed, I never heard the beeping anymore, and I didn't even have to run Photo Booth. The problem is that the beeping came back after I clean installed Mac OS X 10.5.5 a couple of weeks ago. In fact, the problem is even worse now, because it doesn't go away if I turn off CPU2 or run Photo Booth. When I turn off CPU2, I can still hear the beeping. The beeping doesn't occur all of the time, but it does occur very frequently, every day. (I can hear it right now, in fact.) At the same time I installed Leopard, I also installed the keyboard firmware update (which requires Leopard), so that's the other major change from a few weeks ago.