I am importing some .avi files into FCP X. Each clip is about 20 minutes long. The files import into FCP X, but after about 10 minutes the audio cuts out then doesn't come back on until shortly before the end of the clip. It does the same thing on all the clips. If I simply copy the files to my desktop and play them in QuickTime, the audio plays fine. Anyone have any ideas?

Have you tried creating optimised media? Sometimes the data rate of audio causes problems.

Is it possible to transcode prior to import?

Avi files can be very problematic in a program like FCPX. There are dozens of variants that manufacturers use in their hardware for recording AVI files. Some common, some unique to the particular camcorder model. FCPX is obviously not working with this variant. I have encountered AVI files that FCPX will import successfully but only after the program first scans the files and then allows me to choose it for import. Other avi files need to be transcoded. Try using MPEGstreamclip to transcode the files to ProRes.

The important thing is what the codec is, rather than the container.

AVI is a container, not a codec, like Quicktime is a container and not a codec.