Check what actually changed
Use only the filter-access steps intended for the owner. Record the old and new filter part numbers, actual dimensions, filtering rating, and whether the frame is damaged or the filter is dirty. Compare the cabinet instructions with the arrow on the filter. The arrow refers to air moving through the filter, not automatically toward the nearest wall or door.
For its refillable filters, Filtrete notes that nominal size can be labeled differently across brands and says to check actual frame size. That product-specific guidance illustrates why a matching large size label may still need a closer fit check. Filtrete fit guidance.
Do not crush the frame, stack filters, or leave the cover open to improve fit. If the installed filter cannot be confirmed as compatible, ask the provider or cabinet manufacturer for the approved replacement before further operation.
Describe the sound without changing settings
Note whether it is a whistle at the filter slot, a rush of air at a room grille, vibration, or a sound from the furnace itself. Record whether the whole heating cycle is louder or only one part. Include whether comfort or cycle length changed too.
Trane identifies a dirty or overly restrictive filter as one possible contributor to a high-pitched furnace sound. That possibility still needs checking against the equipment, not confirmation from a coincidental filter change. Trane filter and noise distinction.
Do not run the furnace without a filter as a homeowner diagnostic test, change blower settings, or close room grilles to reduce noise. Keep accessible supply and return grilles clear.
Ask for a measured explanation
Have the technician verify the approved filter and the operating airflow conditions. Ask which finding explains the sound, whether the equipment is operating within its requirements, and whether the correction is a filter change, setup correction, or another repair.
Your next step is to send the filter labels and sound timing to the service provider. A useful answer explains both why the filter is suitable and why the sound changed, rather than treating the arrow as the only fact that matters.