After Effects renders with no audio I've been using after effects cs6 to make intros in my youtube template. They always render without sound. I've been exporting them as avi files. I'm currently making one in an mpeg4 format (assuming that is another name for mp4) since my other intros all have sound and they're mp4 files.

I clicked "lossless" in the render queue and I changed the file format to avi. I checked "audio output" and didn't touch the settings inside that submenu and then I clicked OK and render. after waiting a while, AE spit out an intro file thats around a gigabyte in size and has no sound. What is the problem?
The output file doesn't have any sound because there is no audio in the timeline that you are rendering.

The output format (MP4 vs. AVI) doesn't have any effect; both formats can contain an audio track or not. Checking the box to output audio only has any effect if there is already an audio track in the timeline. If there's no audio track, the output will have audio but it will be silent (as you're experiencing).

The solution is to add some audio file(s) to the project and then put it into your timeline.