MOV file plays without audio/sound through Wowza Streaming Engine/Server

Hi I am using Wowza Streaming Engine to stream the video files so users can view the video through HTTP video player. So far MP4 files plays fine, but MOV files can play video without sound. I can play these MOV files locally with sound without problem using QuickTime player 7 or Microsoft Media Player, MPC, QuickTime Player and VLC Player, but when I play the streaming video from the Wowza Streaming Server, the video doesn't have sound:(. Does anybody have any experience about this situation? Thanks!