I just tested headphones on my "new" Mac Pro for the first time, and I noticed that there's some weird blips coming from left and right (randomly) all the time. What is this? I had to put the volume almost to maximum to barely hear it. I read that it may be because of interfering devices nearby (I have the Cinema Display on a table, the Mac Pro next to the table on the ground (25cm from the Display) and an external HDD behind the Display. Thanks!