Published SL MP4 increasing around 20 seconds

Hello I am having issues with a MP4 (interview with audio and visual) is automatically increasing around the 20-30 sec mark. The original file is fine, but once it is published in SL then this increase happens. I have tried to set the volume the same and even tried to manipulate the volume control as well through editing the MP4 file in SL. This is not happening on all files, but I do have about 10 that this has happened on. I have tried to republish but it is still happening. Thank you for any input.