Thanks for bringing this up! This is a known issue that started after we upgraded our audio engine in the last monthly deployment (Version 18.10).
To my understanding, some atmospheric sounds require a new version to be downloaded which normally occurs only when you encounter them during your gameplay session, and can lead to the freezes you are talking about. We have our Audio Programmer looking at this, but in the meantime, you can check the ‘Download everything’ box in Launcher settings to force the game to download all the new files outside of your gaming session.