With extremely high winds, our Opel 2 makes a loud whistling noise.  We do not have an outside air kit.  It's like the wind is blowing across the chimney (we have a proper cap) and pulling or drafting with such a strong negative pressure that it is sucking through every small  crack and crevice in the firebox...making a high pitch whine. If we crack or open the door, it goes away...you can feel the negative pressure wanting to pull the door shut.  Any ideas to resolve the noise?