Apple has released a couple of updates for OS X systems. The first is an audio update for Early 2009 Mac Pro systems that are running OS X 10.6.3, and the second is an updated set of Epson printer drivers. The updates should be available via Software Update for relevant systems, but also can be downloaded at the following web pages.
Mac Pro Audio Update 1.1 (516KB)
The audio update specifically fixes a problem where you may hear audio anomalies coming from inside the computer (no, they weren't ghosts) when using Firewire audio devices. This update will update an I/O platform extension along with a couple of the Intel CPU power management kernel extensions, therefore if you experience any problems after updating you might try resetting the PMU. Additionally, boot into Safe Mode and restart to clear the boot caches and ensure the system properly loads the updated extensions.
While the audio update should be applied for affected systems, printer updates sometimes cause problems for people who have installed them, so if you have a printer setup that works you might be better off avoiding this update. Additionally, Apple supplies printer drivers on-demand, so instead of downloading the whole driver package, another option is to delete and reinstall your current printer.
The full list of supported printers can be seen at this Apple support page.