Video Mic Pro Background Noise

I used my Røde Videomic Pro to record a friend of mine playing some piano pieces for a short film I'm planning to do. I recorded it by plugging the Videomic into my mic input on my 2008 MBP. And then recording it directly using Garageband using the FPS and 0 dB setting on the mic. When I was reviewing the tracks after the recording session, everything sounded fine, very little background noise. However when I tried to export those tracks to iTunes for some reason the background noise level multiplied and became extremely noticeable when I played the tracks back in iTunes. I then tried to export the track directly as an iTunes Plus file to my desktop, I previewed it by pressing the spacebar, and it sounded exactly as it did in GarageBand, very clean sound. However when I import that into iTunes, the background noise level jumped again just like when i exported directly to iTunes. Is it something I did wrong when exporting the tracks?

On a side note I had two Garageband files when I did the recording sessions, and multiple tracks recorded in each files. When want to export the individual tracks I clicked on the headphone button the left of the tracks to mute all the other tracks and export just that particular track I wanted. Would that affect the quality of the final export in any way?