I just got myself a refurbished MacBook Pro, it's a great machine and I am really happy with my purchase. But there seems to be a fair bit of feedback from the headphone jack whenever I plug a pair of headphones in. The noise is basically a low hiss or a low "modem" type clicking sound sometimes. Although it's not that bad with the headphones that you get with the iPod but with my Audio Technica ATH-AD700 you do notice it. I was wondering if this is normal with the previous generation of MBPs because I never seemed to have this issue with my old Macbook (C2D or G4), or should I just take it into the Apple centre because it's only a few weeks old.