I just got AE 6.5 and the exact same thing is happening to me.
I can load a WAV (pcm 44K 16bit stereo) file. If I double click it in the library it opens the little preview window in AE and I can play it there, but if I put it on the timeline it won't play, it won't be heard in any exported movies either, and the sound level value stays at zero.
Some video clips I import that have sound, the sound will work if I export them again. The sound still won't play when I preview the timeline in the program, and most of the time if I do hear the sound on the exported file the sound is jumbled and unuseable.
