Contact them. They will let you download it again. i have had this happen about 4 times (1 album had 4 songs that were bad). Go to
apple support . They usually respond pretty quickly with an email saying you can redownload the track by going to advanced->check for purchased music.
I have had to do this a few times, mostly with losing the internet connection while downloading the songs. I have had pops on my ipod (rarely) but those were fixed by transferring the song to the ipod again.
Edit: If it is a problem with their recording on their side, it may take awhile for them to update the tracks in their data base. If this really is the problem, it will still skip. Just let them know again and they will give you credit. The album i tried to get went from complete to partial and has been like that for several months now. They refunded me for the entire album, even the songs that were good.