When I FaceTime the person on the other end hears a loud buzzing sound. Please help!

Whenever my son uses FaceTime on his iPad mini the person he's calling hears nothing but a loud buzzing sound when they answer.

Model ME276LL/A. Capacity 12 GB. Available 9.23 MB.

I updated it to iOS 9.3.3 and reset the iPad to try and fix the problem but it did not work.