My Osburn insert exhibits a slight wistle as it's running. (not the blower) Can't seem to locate the source. Is it possible that I've got a leak in the connection between the pipe and the stove? I believe I've sealed it with refractory cement. What do you all do to ensure a good seal between stove and pipe? Seems like a tremendous amount of heat there, so I'm not even confident in silicone. I don't have room for an thermometer there. What is the stack temp just at the output of a stove that's really cooking?