Why did my phone all suddenly did s high pitch noise?

[Android Central Question]

I've been calling with my boyfriend and all in a sudden a high pitched noise came out of my phone and if I'd put my volume down then it didn't help and I have no apps that could make this to happen, the only thing thar made it stopped is to restart my phone but I'm worried what caused the high pitch noise comin out of my phone (Android)

 

[B. Diddy]

Welcome to Android Central! Is that the first time that ever happened? Which phone do you have? Was the sound coming from the earpiece speaker or the main speaker?