Haven't posted here in awhile but always cruise through to see whats going on. The stove is an older Regency Insert ,it started making this low harmonic humming last burning season when the stove got up to temperature. doesn't do it all the time . This year I just fired it up and it's happening again.I can put my hand on the stove surround and do not feel any vibrations, before I start tearing things apart I'd thought I would get some suggestions. It's a fully lined stainless chimney. Thanks for any replies