guitar has tremolo sound to it on playback ??

I have been recording lately and on some guitar parts of songs, mainly clean parts on playback it has a weird tremolo effect to it, fluttering sound. I cant figure it out, I had no effects when I recorded, it sounded great in the headphone when the guitar player played it, then on playback it sounds like a tremolo effect was applied or something, here's a sample of what I am talking about http://www.j3design.com/theuniontrade/music/Hopeless.mp3

this song was recorded using garage band 2 , g4 power book 10.3.9 , 1.33 GHz, 768 MB RAM, fire wired to a presonus firepod do the guitar direct in.

I also had the same problem on a clean guitar recorded with a mic in front of the cab, same tremolo effect on playback.

Here are some things I tried, thought maybe it was my computer, so I burned it on a cd, same thing. I took off all effects, even on the master track, still the same.

The firepod is brand new, I used different channels for both the songs and they were recorded differently, same problem.

Has anyone had this problem?
If so how can I fix it so it does not happen again.

Thanks


g4 powerbook Mac OS X (10.3.9)