Mark, can you provide more detail about how you’re doing this in Final Cut Pro? What digital camera are you using, and what version of Final Cut Pro do you have? When you placed the video into your Timeline, did Final Cut Pro warn you that your sequence settings didn’t match your video settings? Also, are you seeing a red line along the top of the Timeline?
A red line means rendering is required, and you will probably see this, because you’re using formats that Final Cut Pro doesn’t handle smoothly. For example, you’ll get the best results by converting your .mp3 files into AIFF (48Khz, 16-bit) files. “MP4 video files from a digital camera” probably means you have H.264 files. When you right-click on a clip in Final Cut Pro and choose “Item Properties–>Format,” does it say H.264?
Anyway, if you can provide as much information as possible, I’m sure I–or some of the vastly more experienced people here–can help you out.