Audio is obviously an important part of human communication. Our language and ability to communicate in that way is largely what separates us from the chimps. For a student, hearing a comforting voice late at night as they study might just be the added human element they need to connect to the content. Online courses can easily have your voice added to them using any of the tools below.
SoundCloud is a great tool for sharing audio. Here is the Getting Started Guide and an example below. It is also web based so you can quickly record the audio and embed it into your LMS or any other HTML location.
With Audacity you can add an mp3 file to your course management system as an attachment that students can then play from the web or download onto an mp3 player. Here is a downloadable mp3 file. example
This page from Articulate and the Rapid elearning Blog has some exceptional links that you might use.