I am new to having a heat pump, this is my first winter. Last night was the first night below 20f outside that I was using the heat pump. The heat pump makes a growning sound for a few seconds when it begins the defrost cycle like the compressor is straining to start. Last night the sound became very loud to the point it woke me up. Sure Comfort 3.5 ton single stage HP. Is it normal for the compressor to strain more to begin the defrost on a colder night? Normal startup sounds fine, only notice the problem when it goes into defrost.
Prior to last night I had switched to aux heat below 30F but in other posts I was convinced the HP was economical to use in lower temps. It still made the straining noise in with temps in the 30s but no nearly as loud as it did last night when temps got below 20F