It's likely the the inducer has been thrown out of balance - fan warped or something from pulling out a dead bird.
BTW, when I installed a new evap coil with the new heat pump, I removed a canvas collar, so now it's a ridged connection to the main trunk. This was done right after the bird find... and until now, the furnace hasn't been running because the heat pump has been used. I wonder if I install a new canvas collar, if that might solve the problem.... Any thoughts on this?
I took it out when I installed a new cased coil for the heat pump. The new case was about 2 inches taller, so it was removed.Yes, no matter what is causing the noise it will be transmitted way more strongly through a rigid plenum connection. Why did you take out the flexible connector? It was there for a reason....
Thanks!Turn the gas valve off just before the furnace. Turn on the furnace and let it cycle a bit. (it should lock out, so you'll have to power cycle after turning the gas back on) If you hear the rumbling as it tries to cycle on, it's the inducer, as we've now discounted the indoor fan and any firing issues. (the indoor fan shouldn't run until after the furnace has at least tried to fire. Some won't come out until a bit after it has fired)