Some "cam" sites stream their videos using non-standard audio and visual combinations. In particular the SPEEX audio codec.
Consequentially, while Jaksta Media Recorder will save the entire stream, it appears as though there is no audio present when played back.
The simplest way to reveal the audio is to do a conversion to another video format such as MP4 Default (MP4).
Many of the MyFreeCams feeds use SPEEX and other audio codecs that most players wont play back.
A conversion to MP4 will take care of it.