The heater is less than 1 year old and just started making a whistling noise when heating. I did some research and thought it may be caused by a faulty unitherm govenor. I removed the unitherm govenor and the heater ran silently. I purchased and installed a new unitherm govenor and the whistling is back. Any ideas about what else may be causing the problem? Is it OK to run the heater without the unitherm govenor for short periods of time?