I have 15" G4 1.67 model and occasionally couple keys stop functioning, they are o, l and . plus one function key, for keyboard brightness. Sometimes those kes work just fine. When they don't, I have noticed that when I try to adjust volume there is heavy lag and I hear popping noise from speakers. The machine does not crash, it functions fine otherwise. I have not yet disassembled the machine but has anyone here had these kind of symptoms with their powerbook, any tips? I'm hoping that it would just be loose keyboard connector or something.