Hello, I recently purchased a used vista flame 2008. when its running it will come out with a ringing sound it does not last long, about a minute or so, it may do this two or three times in 5 or 6 hrs of running, It willl make the noise even in shut down mode, so iam lead to believe its not the feed auger, anyone have this problem before, its not so much a big deal, I am just curious,being new to pellet stoves.