Unwanted sound when a key is pressed

I have a custom view that accepts key input, inside NSScrollView. I set acceptsFirstResponderto yes and it successfully accepts keyDown. But every time I press a key, I hear a beep. I am sure that there is something else, but I don’t remember that .. Please help.

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

NSLog(@"is first responder %i", self.window.firstResponder == self);

switch (theEvent.keyCode) {
    case KeyCodeEnumBackspace:
    case KeyCodeEnumDelete:
    {
        if (self.scheduleControl.selectedEvent) {
            [self.scheduleControl deleteEvent:self.scheduleControl.selectedEvent];
        }
    }
        break;

    default:
        break;
}
   }