I have a 4ton Gibson heat pump 13 seer installed Jan of this year,
when it was first installed, I would hear only the outdoor fan blowing wind noise, and hardly hear the whining.
recently I noticed the when it first startup, no whining noise, just fan noise, but after about 15 or 20 minutes of runtime, the whining noise become more noticeable. this louder whining noise on outdoor unit begins about 1 or 2 weeks ago
it is still producing good heat, I set the thermostat to 74F while outdoor was 22F, and went down to basement and feel the insulated bigger copper pipe, it was hot to touch, and the smaller copper pipe was warm to touch.
would a dirty air filter or warmer return air cause outdoor unit to whining louder? or vibration caused some casing panel or screws to come loose?