Does the problem persist when you convert a particular file/files of a particular format/every file?
If this is a certain file or files from the same source, please open one of them in AVS Video Converter, choose the preset, then click on Advanced > File Information and attach a screenshot of this window.
Have you tried playing the converted files in different players?
When you preview the source file in AVS Video Converter (in Edit window) is there sound?
Hope to hear from you soon.
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