Having Microphone Issues on FaceTime and Skype?

I have tried to use both FaceTime and Skype on every device in the house (windows phone, android phone, two different iPod touches) and on each one there is a white noise that makes a horrible screeching sound and makes the call impossible.

It never used to do this, and I don't know how to fix it. It works on the smart tv and on my own laptop without white noise, but anything to do with the microphone on other devices just creates the white noise.

I've already reset the settings on both iPods, and I've checked the sound levels using the recorder, and it's picking up no white noise.

Does anybody know how to get rid of this white noise? As I've said, it used to work fine.

(iPods are 5th and 4th gen, windows phone is a Lumia 635 and android is something I don't know, sorry)

The only thing that I know has changed is we've changed wifi providers from Sky to BT, but that's it.

Help, please!