Some people, including myself, have reported a very loud noise being generated during attempts to use VocalSync.
 
I gathered up the courage to try it again, and sure enough, I got a horrendous noise that I thought was going to blow my Adam 7's.
 
I tried changing the output from the two vocal tracks to the main outputs of my interface (instead of the Master bus). No noise, and VocalSync worked well.
 
I don't understand this "fix", but you can bet I'll be switching outputs before using VocalSync again.
 
Obviously, it sounds like there is some kind of feedback from the Master bus to those tracks. I've looked, and I can't find anything that would cause that.

Some people are getting this, some say they can't provoke this.
I can't.
Those that are getting this, does it happen immediately? After you do something?
Are there repeatable steps to reproduce this? Size of clip affect it?
Some sort of sequence of actions?
Does it happen on slower machines? Faster machines? Core settings?
 
There's a thing called a Cerberus Audio - Ice9 Automute, recommended
by a member. I downloaded it, but have yet to use it in anger.
It mutes to protect your ears and monitors.

For me, it happens as soon as a VocalSync Region is created.
 
It doesn't always happens. If I start a new project with nothing in it, import some audio and try it out, it works OK. Usually.