Hi

We need more information to help diagnose the issue with the sound you are having:

The specification of your computer system including Windows version and program version, see this topic for what is required and please quote processor and graphics card make/model in full, and also what monitor/screen resolution(s) you are working with if this is a laptop.

I would suggest you put this information in your profile signature so we do not have to keep asking for it.

Are you are using an external sound device/system, if so what is it and, if USB, are the drivers up to date and set as the default Windows playback device?
 
What video format, codec and resolution are you using - to help with this download and install MediaInfo one of the clips causing the issue and post the results, see this tutorial on how to setup MediaInfo and analyse a video clip for all the data required.   

John EB
Forum moderator