Hey Pelton -
Thanks! I'm a rookie but willing and able to learn. I tried tightening everything down and using the 'dollar bill technique' and conveniently enough it seems to have done the trick for now. If it springs back up I'll dig a little deeper with the new thermostat issue, There's a semi-modern t-stat on the 2nd floor that was here when we moved in, that's why I felt the one I installed would be ok.
Thanks again! Happy holidays!