I don't recall losing sound, but I do remember that there are some audio output options in the Roku menu. (Settings > Audio > Digital Output Format.) You might want to try some of those and see if you get different results.
Sorry, been there, done that.
I am having the same issue with two different Roku's, and I have changed the cable also.
Brian
Not the cable.
Thanks. I just need to hit the back button on the remote and get back what I am viewing. It is a little louder than it was but then it calms back down to the correct level. Sometimes does the a couple of times a night. I have updated the device so it has the most current version.