Why do my phone calls sound weird?

I have an iPhone 6 plus, not 6s but regular 6 plus and I just 2 days ago updated my phone to iOS 10. Since I updated my phone my phone calls have sounded weird, it almost sounds like I'm trying to talk through a tin can. Before the update my phone sounded completely fine. Why did this happen to my phone? Was it the update that did this, if so how can I fix it?

How did your carrier answer your question?