Without details I have no idea what's going on. It is not normal, but I don't know anything about your experience level, your system, your project, the type of audio file or anything else about your project. You might have just as well asked "Why is watermelon?"
What Rick said - audio prefs, what audio ius used, project settings, system info and so on.
In addition to the other information requested, exact version number of After Effects would be nice to know too.