The correct way to disengage the autopilot in the RJ is to press the red AP DISC button on one of the yokes. If the autopilot has been forced off by other means, the autopilot "cavalry charge" audio can also be silenced by pressing the AP DISC button on the yoke. This can also be triggered using the TOGGLE DISENGAGE AUTOPILOT or TOGGLE AUTOPILOT MASTER control assignments.
It may also be worth considering that the Autopilot DISENGAGE switch on the MCP is only typically used in an emergency. If this switch is activated, the autopilot cannot be reengaged until this switch is returned to the up position. it may cause the autopilot "cavalry charge" audio to play until the switch has been reset and the AP DISC button pressed.
Hope that helps.
Mark - Just Flight