Owners of the Mac PowerBook G4 are experiencing an audio defect in their high-resolution, 15- and 17-inch models. The problem, described as a looping echo sound that magnifies itself for about four to five seconds while playing any kind of audio or video, was also reported in 12-inch notebooks. There are also numerous reports that this problem occurs in other Apple computers such as the Power Mac G5, iMac and iBook. A group has started an online petition to demand that Apple take action and solve this problem. If you're experiencing these difficulties, head on over here to sign the petition.