Ok, so you know that sound external flashes make when they charge? That high pitched whiiiiiiiiiiine? My SB-600 is making that noise with freshly charged batteries all the time. I was photographing an event the other week and I had charged my batteries the night before, but they kept running out during the event. I think that was an issue with the rechargeable batteries (they were quite old) rather than the flsh. Since then, I got another set of rechargeables, and the flash seems to work ok, but constantly has that horrible whine. I know something must be wrong, but is it a serious problem?