Not the first time this had happened, I’ve been out camping where the temps were in the low 20’s at night, furnace went all night long and worked flawlessly. and kept the water from freezing in the underbelly, Got home and decided to let the furnace run and winterize the pipes later. Well it made a horrible Noise and vibration at start up and I thought it was going to fly apart. I started to tear into it and try to isolate the issue, I pulled the squirrel cage cover off and their lies the problem.

 

 

Hmm, doesn’t look like a squirrel cage. 

Yuk.

 

Someone should look at screening the intake and checking the floor where pipes and stuff come up from below. 

That’s the most elaborate mouse trap I’ve ever seen!