I get the same problem all the time. It typically happens for me when I have too many video + audio files in the timeline. I'm not sure of a solution, but as a "temporary fix", I just make sure to preview only a small amount of it.
I'm not sure if you're aware, but you can highlight a certain amount of video/audio in your timeline (depends on what your viewport settings are at, such as best, average, etc. you can check on the top of the viewport) and shift+b to render the highlighted section in Vegas and it will automatically preview it for you. This doesn't temporarily solve the small freeze problem, but I usually don't need to worry about the audio cutting out since I never preview a long period of the video.