The problem is that MP3 format adds little silences at the beginning and end of tracks.
Open those files with a Wave Editor, and you'll see it.
You have to delete those silences manually.
To burn those WAVs you'll need to use Feurio! and "Do not insert pauses between tracks" Setting (or link the tracks), because their length won't be a multiple of a CD-DA sector (588 samples).
I also recommend Feurio to delete the silences.
Drop the WAVs in the project. Open Track Editor, zoom to the end of the tracks, and use the "Set end position" (Action menu) tool to select the end of track. (the same for the beginning of tracks).