HEy...thanks for helping me clarify Glenn. I am definitely learning on the go here. It is my understanding that they installed the heat pump to the furnace. The heat pump does the AC and Heat unless the outdoor temp gets too cold. Then, the gas furnace kicks in. Does that make sense. When I saw the exhaust the gas furnace was running. I had the thermostat set to Emergency Heat so I could see the exhaust...I had physically inspected the flue as much as I could and figure that might be helpful.
The sytem shut down again last night after about 2 hours of normal use...it had only kicked on once in that time. Then, it started with the hum only again. We shut it down for the night by setting the thermostat to off. When we turned the termostat on this morning it came on like normal.
Thanks again for your help Glenn!
ps...here is a blurb from the service company that installed the pump...
"Carrier's Hybrid Heat™ delivers peace of mind to homeowners concerned about the
unpredictable nature of utility costs. Hybrid Heat pairs a gas furnace with an electric
heat pump to provide comfort, economy and flexibility. Your Carrier Hybrid Heat system will automatically switch between electric and gas heating as needed to keep your home comfortable all winter long while optimizing the efficiencies of each fuel source. And, because the heat pump also delivers cool comfort when it's hot outside, your Hybrid Heat system is a complete, year-round indoor comfort solution. Ask your
Carrier dealer if Hybrid Heat is right for you."