The Autopilot Disconnect 'Cavelry Charge' will continuously play anytime the Autopilot has been disconnected via non-normal means. 

The correct way to disengage the Autopilot is to use the AP DISC button on the yoke. In MSFS, the TOGGLE AUTOPILOT MASTER and AUTOPILOT MASTER OFF control assignments can be used to trigger the AP DISC button. Triggering either of these control assignments or clicking the AP DISC button will silence the warning.