I just got my iPhone 3GS replaced under warranty and just turned it on because I just got home. The first time I hit the vibrate switch, it started vibrating and now it won't stop. I'm restoring it right now, and it's still vibrating. I rebooted it with home+power, which only caused the vibrating to stop during the few seconds that it was powered off. When it turned back on, it started vibrating again.