I can hear the sound of my footage (shootng 720/24p) on the speaker monitor, but not when I go to FCP, my A/V settings are on 'default' for audio, when I change it to 'built-in' it still doesn't do anything. Any ideas? Thanks.

if you're changing it to built in audio at the upper toolbar under view, then make sure under audio video settings it is on built in audio as well. Or firewire/dv, depending on your desired output, sometimes audio video settings is setup differently then what the toolbar shows. hope this helps.