A common problem
A slight sound change when modes switch can be normal, but new rattling, scraping or strong vibration should be checked.
Without opening the casing, note:
When the sound occurs — at start-up, during fan operation or at the outdoor unit.
Whether an object near the outdoor unit could be vibrating; do not reach through the grille.
Record a short video or sound clip if it is safe to do so.
For metallic scraping, loud rattling, increasing vibration or noise accompanied by a burning smell, switch the unit off and request an inspection.
Do not remove covers or touch the fan; it may start unexpectedly. Do not tighten electrical or mechanical parts unless qualified.
A better project. A cleaner installation. Fewer unforeseen costs during construction.
