Hey, I have a Late 2013 MacBook Pro and recently when I plug in my iPad or iPhone in either USB ports they start charging then stop then start and stop. After a while this stops happening buts its really annoying. I have tried about five different cables and its the same problem. iPad and iPhone charge fine using the wall plug and external HD drives when plugged into the Mac are fine and don't have the problem, just the iPad and iPhone. iPad is almost brand new also. Any ideas?