You should be able to preview audio.
In the Preview Panel, is the audio icon enabled ? If you press the "." key on your numberpad, do you hear audio ?
Is your layer "audio switch" activated ? (the little headphone icon near the eye icon).
Is your Sound card properly setuped in the preference menu (edit > preferences > Audio)
Have you ever heard any sound in AE, or is it the first time it has happened ?
In addition to Sébastien's questions: What is the source format of the files? Maybe the audio is encoded in a way AE can't understand or it's multichannel audio, where the audible info is not on the first two channels (AE realyl only does stereo at best)...