Heat Pumps and Electric Heating - Goodman unit/AuxHeat?

I have a relatively new (6 months) Goodman unit that was installed for a room addition and also feeds an upstairs bedroom. I've noticed about 5 times in the past 2 weeks that the outside unit's fan will stop blowing and the thermostat will switch from reading Heat to AuxHeat. After about 5 minutes the fan on the outside unit will again kick on and the thermstat will go back to saying Heat. During this 5 minutes that the fan had stopped on the outside unit, the heat was still blowing from the vents. I was outside once when this happened and heard the unit give off a loud sound that sounded like compressed air being released prior to the fan stopping. About 5 minutes later the same loud air sound happened again and the fan then kicked on again. Also during the time the fan was stopped, the unit was giving off a pretty loud electrical humming sound. Is this normal behaviour?

100 percent normal. Your heat pump went into defrost mode to deice the coils. If it did not do this your heat pump would eventually turn into a big block of ice - literally. When your heat pump is in defrost mode it turns off its fan and reverses the flow of the refrigerant (which is the noise you hear) to heat up its coils. Also at this time your AUX heat kicks in to continue to heat the house (and your heat pump steals some of that heat to heat its coils and melt any ice).

When its done defrosting the heat pump will reverse again and the fan will kick on and sometimes you will see water vapor blowing out through the fan when it starts (it almost looks like smoke, not to worry though).

The other noise you hear is just the compressor. Its just more obvious to you when the fan is not running.

-Doug

Aren't the elect. elements after the heat exchange coils? if so how can they benefit the defrost cycle ?

Thank you, Doug! Thanks again! (it says I have to use 25 characters) :)

Yeah the aux coils are typically past the evaporator coil so the gain is minimal for the heat pump, it is more of a comfort issue with the air coming from the vents being uncomfortable to the house inhabitants