Final Cut Express HD (3.5.1) and Snow Leopard

I use my MacBook Pro (2007) in recording live music using Logic Pro. No problem ever found. Recently I had to mix some recorded music with some pictures and films, so I decided to use my Final Cut program, which was perfectly working with the old Tiger. At the moment i have the latest version of Snow Leopard. Anyway, when I import sound files into the audio region of Final Cut I can hear just some tics or pops, like a metronome. No music, even if the file is there and visible.
Is there anybody able to suggest me something (maybe I have forgotten some tricky setup), or is it a compatibility problem? Have I to upgrade Final Cut to a new version? Thanks for any reply.
Franco