For a while now I discovered that VoiceOver increase and then decrease in volume when I interact with my iPhone 6S running IOS 10.3.3. When I open apps like Mail and Facebook I encounter that the TTS speech gets louder and when I close apps again there is a decrease in the speech volume. It happens with all the voices I use like Tessa, Oliver and Ava Enhance. I do not experience any such problems when listening to music and audio books and videos. I turned off the phone and back on again and also tried rebooting by holding the Home- and Sleep/wake buttons for ten seconds, but no luck. Does anyone here encounter the same situation?