Tom, I am definately by no means an expert onn the DIGIQII, but in my experiences, I only leave the top vent open about a 1/4 of the way. I have been told that this allows the blower assembly to do its job, as Ed Jones has stated though you may have an air leak elsewhere. I would start at your access door and go from there, but at least try to shut the top vent down to just barely open, and see what happens.