Unwanted beep when a key is hit

Got it. The beep occurs at keyDown, not at KeyUp. To remove the beep, I need to handle it, and an empty implementation will suffice. The key is not to pass it to super

- (void)keyDown:(NSEvent *)theEvent {

}

- (void)keyUp:(NSEvent *)theEvent {
    switch (theEvent.keyCode) {
        case KeyCodeEnumBackspace:
        case KeyCodeEnumDelete:
            if (self.scheduleControl.selectedEvent) {
                [self.scheduleControl deleteEvent:self.scheduleControl.selectedEvent];
            }
            break;
        default:
            break;
    }
}