The brake on all dewalt saws is electrical and is controlled by the switch.
When the switch is released, for a split second the polarity going to the motor is reversed. This causes the brake action. Good motor brushes and brush seating are also critical for this process to take place.
The noise you are describing sounds like bearing noise, possibly at the fan end of the armature or the spindle drive pulley.
DeWalt has a service network nationwide and can be accessed at DeWalt.com
and has a link to Dewaltservicenet.com you can view schematics and bill of materials as well as order parts online