The app button isn't working on my S6. All the other buttons are, but not this one. Any ideas?

[AC Question]

I fell asleep and woke up, checking my phone. The app button wouldn't work. It's overheated fairly quickly too. I tried a system re-boot, but no luck. It also made a strange squeaking noise.

 

[B. Diddy]

Welcome to Android Central! Does this happen in Safe Mode as well? https://support.t-mobile.com/docs/DOC-29226. When do you hear the strange squeaking noise?