Remove Silence from *Beginning* of Recording

I was wondering if there's any way, in GarageBand to 'set the in-point' or remove some silence from before any of the tracks start playing. I recorded about 10 tracks for a song, and the first track starts about four measures into the song, leaving a really long silence before any sound is heard.

Is there any way to cut that silence or to move the all the audio tracks towards the beginning of the song, preserving all the volume/pan rubber band points I've placed in the song? I did a lot of work getting levels right throughout the song, but I cannot get the volume and track pan rubber band points to move with the recorded audio when I move the tracks! I know that I can set the purple end marker to mark the point where GarageBand ends the song... but is there anything similar for the beginning?