Normally GoToMeeting is trying to block system sounds that might disrupt the presentation. Depending on what kind of hardware you're working with, this document may give you some insights: https://support.goto.com/meeting/help/how-do-i-optimize-my-computer-for-video-sharing-g2m090150
What you may also consider is using training Activities to share specific videos with your audience: https://support.goto.com/training/help/learn-about-activities-and-breakouts-g2t040023
Some users have stated that the Labs video tool is more compatible with videos at 24 frames per second, with a Constant Framerate. Hope this helps!