Record the shutdown pattern
From outside the closed equipment, note when the thermostat stops calling for heat, when warm airflow changes, when the sound begins, and when it ends. Describe whether it is a hum, scrape, rattle, whistle, or single bang. Record whether the noise is new and whether heating performance has changed.
Do not open the furnace to identify the sound by touching a motor, tightening parts, or stopping a moving fan. An existing safe recording is useful. Repeatedly cycling the furnace to reproduce a worrying sound is not.
Trane's noise guidance distinguishes mechanical, airflow, and ignition-related sounds. Those categories help a professional direct the check, but an online recording cannot establish which applies to your furnace. Trane sound distinctions.
Ask for a focused inspection
Give the technician the timing record and ask which component is active at the moment of the noise. Ask what confirms the finding, whether the sound comes from the equipment or an attached surface, and what would address it.
If a motor is recommended, ask how its condition was established. If mounting or vibration is the finding, ask how the correction will be verified through the same shutdown event. A part label or the furnace's age is not a diagnosis.
A new, severe noise deserves prompt service. Trane advises shutting down and requesting repair when normally quiet equipment suddenly becomes loud. Trane changed-noise guidance.
With no active gas or CO warning and safe access, use the ordinary owner control to stop heating while arranging prompt help. Do not approach unsafe equipment.
Your next step is to book a check specifically for the shutdown sound, with the record of when it occurs. Ask for the correction to be checked against that same pattern, so the reported problem stays at the center of the visit.