If you installed Mac OS X 10.4.10 before 02-Jul-07, you probably got version 1.0 of the update, which caused some Intel-based Macs with external speakers to experience "popping" sounds. PowerPC-based Macs weren't affected. (For details on what was fixed in Mac OS X 10.4.10, see "Mac OS X 10.4.10 Released," 2007-06-25.)
Apple has now released a variety of updates to address this annoying problem. If you haven't yet installed the Mac OS X 10.4.10 Update on an Intel-based Mac, you'll now see a fixed version 1.1 in Software Update; it's also available as a standalone download in both delta (72 MB) and combo (297 MB) forms. Those who have already installed Mac OS X 10.4.10 will instead see Audio Update 2007-001 in Software Update; it too is available as a 660K standalone download.