Siri unable to hear

I'm currently having issues with Siri being able to hear me on my iPhone 6s since updating to iOS 10.

I've tried a hard reset (home button + lock button) which hasn't resolved it which made me think that the mic had gone. But doing some research, Siri/Dictation use the same mic as the ones used for FaceTiming. So I've FaceTimed someone to find that they could hear me perfectly well. I have also turned Siri off and used Voice Control which was able to hear me and respond accordingly.

Could this be a software issue, and is anyone else experiencing such problems? Is there something else I can try?

Thanks