I have a Castile insert, and every so often it makes a loud vibration sound, almost sounded like it was growling so I sat next to it and waited until it was making that noise, and it appears that on mine when the stove gets hotter, and at certain RPM's it gets a vibration, because I had my hand on it and I could feel the vibration happening, and the noise appeared to be the top baffle plate rattling a little, so as it was making this noise I took the door handle and was going to open it briefly and I noticed that as soon as I just lifted the door handle a little bit the noise stopped. So I took a small piece of aluminum foil, folded it and turned the insert off, and when it was cool enough I opened the door, and I pushed up the top baffle slighly and I tucked this small piece of foil where the top baffle plate rests against the unit in the front by the door. This seems to have cured the growling sound, but I'll be asking my installer to get a new blower assembly that doesnt vibrate and install it because Im still in the warranty. I believe that the top baffle plate is slightly warping as the stove heats up and that slight uneven condition causes it to rattle when the blower gets the vibration.
I believe that as the unit get hotter the blower cage must expand slightly and its out of balance, and it takes that certain RPM point to make it vibrate, and when it does the baffle rattles. On mine it seems like it only growled at certain motor speeds, the blower speed varies by a few rpm with the AC line voltage, and its my opinion that it hits that certain spot every so often and vibration occurs. check to see if your top baffle plate is seated snugly.
