imovie 08 audio snafu

okay, here's the situation.

i'm making a movie in imovie 08 and having problems with audio overlap.

the movie is approx. 28 minutes long. i have some clips at the beginning of the movie that were shot on a porch, with voices and birds chirping.

now, i put another clip in at the end of the movie, at least 15 minutes after the clips at the beginning, and the audio on the aforementioned clip is from BOTH clips. the clip at the end is a shot of some fireworks, but i can hear the conversation and the birds chirping from the clip that i put in at the beginning of the movie.

there is no audio track on the second clip except for the audio that was actually recorded with the clip. so there's nothing to delete... i tried ducking all other audio just in case it was giving me some kind of invisible audio clip, but that didn't work either.

using a white macbook 2.1 (not my machine, client's...) running snow leopard, certified mac technician, no clue how to approach this. any ideas?

thanks in advance!