Our P61A recently started doing something out of the ordinary. When the stove is calling for pellets and the fire is burning, everything is normal. However, once the stove no longer call for pellets and starts letting the stove cool down, we are getting this weird vibration sound every three seconds or so. It's almost like a pulsing sound. If I turn the temperature up or move the dial to "Off" the sound stops. Not quite sure what is causing it or how to fix it. Hoping someone out here can help. Thanks in advance.