Englander 10-CPM Heat Exchange Box Vibrates When Hot

I have a 10-CPM that develops a vibration in the heat exchanger when the temperature at the vent exceeds 145 degrees (or depending on the type of pellets when it is at Burn Rate 7/Blower Speed 7 or above) I finally located the vibration yesterday – there are slots on the top cover of the stove in the front, I used a slim screw driver to go through the slots and put slight pressure on the the top of the heat exchanger box (which is an inch and a half under the top cover). The vibration immediately stopped, removed the pressure and the vibration resumed. With tech support on the line I removed the stove's top cover...saw nothing outstanding that could be causing this. At his advice I blocked 1/4 of the OAK's opening and lowered the Low Burn Air setting to 3...same problem. Just wondering if there is someone who experienced something similar and would be able to shed some light on this problem.

Thanks - G.B.

Thanks for your response on this issue, I worked with tech support (Patrick) who have concluded that there is a possible broken weld somewhere in the heat exchanger box. We are currently working out the logistical details of a swap, I am glad to be receiving another unit but I am not looking forward to the work involved as the stove is on the 2nd floor. But, things could be a whole lot worse. I do really like the 10-CPM and am looking forward to eliminating the vibration problem.