No voice feedback when using Siri with American accent in iOS 9.0.2
Siri and "Speech" on iOS seem to be tangled since iOS 9. Here's how to fix it:

Go to Settings -> General -> Accessibility -> Speech -> Voices -> English -> and download both "Siri Female (Enhanced)" and "Alex".

Note: Make sure to stay in the settings app while the download is completing. If you leave the app or go to another page within settings, the download will cancel.

Let me know if that works ;).