Didn't even know Maya could render to AVI. It's generally a bad idea to render as a movie file instead of an image sequence; if the rendering fails while outputting a movie, the entire movie will probably be unplayable. If it fails/crashes after rendering 950 frames of a 1000 frame sequence, you just need to re-render the final 50 frames.
You'll need to add the sound using another application - Maya's really not built for producing final output with sound - it's part of a production pipeline before it gets tweaked/comped/graded/edited etc. for final output.