If any noise or vibration starts or stops when pressing the brake/clutch it usually indicates a problem with the upper drive belt or power train.
I would take the deck off and jack up the rear to be SURE it cannot move to run over you.
Crank it and have someone partially depress the brake pedal, being careful to not move the mower off the jack!.
You will see how the brake pedal releases tension on the belt, which btw is handy to change or adjust the belt.
Releasing tension on the drive belt stops driving the transmission, thus working like a clutch.
You probably will see where the noise is coming from.
Bad idlers squeal when turning. A spring tensioner may be missing.
Worn out belt, damaged or loose pulley, adjustment needed or whatever.
All of this will not be exactly related to your exact mower, but just general information.
Cub cadet and the cheaper mowers use cheaper idlers that may not last long at all.