I'm actually having this issue since updating to iOS 9.3.3. If I turn the volume on Siri up, it doedn't stay. It seems to be connected to my volume control in CC now. Before 9.3.3, if I set Siri's volume, it would stay on whatever I set it on, no matter if I turned my volume down on music, etc. Now if I turn the volume down, Siri's volume goes with it. It should be independent, right?
I've tried a hard reset, turning Siri off and on, reset network setting, turning dictation on and off, different Siri voices, and the issue still persists.
Any ideas?