I have two M8 OTT TV Boxes which have been working perfectly, for quite a while. Then one day, for no reason that I can think of, the sound disappeared on one of them when using Kodi. I was getting sounds when on the Android screens, but when I was using Kodi v16.1 Jarvis, I did not get the clicks or the whooshing sound when making selections, as well as there being no sound on any video, very frustrating.
I Googled for possible solutions, but nothing seemed to work. Then I realized that I should compare the settings on the two M8 OTT TV boxes and found that on the Android Home screen under Advanced that the Digital Audio Output values were different. The working M8 box was set to PCM with Auto Audio Detection set to ON and the non working one was set to HDMI with Auto Audio Detection also set to ON. I found by changing it back to PCM cured the problem.
By the way I have ALWAYS used HDMI cables to link the Box to the TV.
Change Digital Audio Detection to OFF then you are able to change Digital Audio Output to PCM
Change Digital Audio Detection back to ON
Success, everything started working again It really came down to keeping the Digital Audio Output set at PCM
I hope that this works for you. It was very puzzling how this happened in the first place