The actual rear of the phone is made of shiny black plastic. (techradar.com)
There's still a camera bump too — this is easily remedied with a case, but for those wanting to show off the new glossy rear of the phone it increases the chance of damage when you place it on a flat surface. (techradar.com)
As for audio, I played Rihanna's new video for the upcoming Star Trek Beyond movie and found that the slim but powerful speakers at the top and rear of the phone blasted Ri Ri's killer sound without any muddiness. (tomsguide.com)