We recently bought a brand new Hearthstone Pheonix directly from a dealer in New Hampshire. We are still in the "breaking in" process (4th burn) and it appears there might be an air leak. Last night and tonight, it did the same thing....when it gets up around 250 degrees, it starts making a whistling sound and moisture bubbles up between 2 of the soapstone plates (on the top). We have read through the entire manual numerous times but can't seem to find the problem. Any advice is greatly appreciated. Thank you.