I believe I encountered your same problem. Just coming from Premiere where my audio always played I was baffled by the lack of audio in AE. As it turns out, it's just wired differently than video editors like Premiere og FCP. You can only get sound when you've got real-time playback, and that's not too often you get that. In video editors you'll get audio in realtime, and your video preview will just skip frames to keep up, but in AE ALL frames are played so the 'real' time is adjusted and AE just won't bother with adjusting the tempo of the sound to match up. I believe that is what you are experiencing. If you instead do a RAM Preview (where AE will do a quick render of ALL frames in the selected area before playing back) you will get a video playback in realtime and then the audio will get played as well.
But on the other note. Sometimes I wish I could just hear my audio like in my video editor and just let AE skip the frames it can't keep up with. I don't know if that's in any way possible.