I plugged my iPhone into my Macbook Pro to recharge it. As usual, the iTunes window appeared and syncing began, but the phone kept beeping. I unplugged it and used the same cable to plug into an electrical outlet and it's charging just fine with no beeps. What is causing the beeping when I connect to my laptop and how can I fix that? No problems for the past 3 years. This is a new one for me and can't find a solution. Thanks much!