Loss of sound on video when uploading from Rush

Hello,

I have started loosing sound on my videos when uploading from Rush to my C/.  I have plenty of space left in my drive and check the sound before uploading.  

It does not happen all the time and when it does it loses sound in small amounts though out the video, but sometimes as much as 10mins of sound is effected.  

My recordings are hour long.  I haven't had this problem before.