I’ve noticed that several “kindle fire hdx” owners have had trouble with a loss of sound. This happened to me and it took me at least 6 months of trial and error to figure out the problem. Apparently if the back of the case warps, this causes some kind of electrical problem resulting in no sound. I discovered that pushing gently on the back of the case solves the problem. Calling the top the end with the ear plug jack I found the ideal place on the back to push was 1 1/2 inches from the top and approximately in the middle. The exact location is probably not important, you just need to take the warp out of the back of the case. I then made a bracket with no. 9 wire and shrink tubing that hooks on the edges of the kindle and holds the back flat. Maybe some one at “ifixit” knows why this works.