I wouldn't call this a problem, but I noticed something interesting about my PowerBook G4 last night. I'm travelling so in the evenings I've been using it as a very expensive stereo system -- it has all my music on it. Anyway, I'd had it sitting on the bed running on battery power for maybe an hour when I noticed there was a little crackling coming out of the speakers. (If I'd been playing a CD I'd have thought maybe there was something wrong with the CD.) I was reading and didn't want to stop mid-chapter so it was awhile before I got around to investigating. I thought maybe since it was sitting on the bedspread it wasn't getting good airflow and might have been overheating, so I put it on top of a hard binder -- no change. But the moment I picked it up and put it in my lap the crackling stopped. It's been fine ever since, although I haven't had reason to try to repeat the "experiment."