That "scream" is the brush being pushed down a very dry bore, just like going down a metal slide and ya bare legs hit it, you get that squeal!I hope that was a good enough example for you.
I get it sometimes when I use Boretech with a bronze brush, hard on the brush, but man it rips the shit out of any fowling quick!!
Nothing to worry about, a copper bullet doing 3000 FPS ish down there will be a lot harder on the barrel than you will ever be,with a bronze brush and a cleaning rod
PS And if you dont know what the hell Im on about with the slide please dont go hanging around kids play grounds "honest officer I was only listening for the squeal!!!!!"
I will not be held responsible LOL