Furnace occasionally makes a high-pitched whine during operation.

Safety: Turn off power before inspecting blower or inducer.

Steps:

• Open registers: Ensure supply registers are not nearly closed, which can cause whistling.
• Check duct joints: Listen for whistling at duct seams and seal gaps with approved foil tape or mastic.
• Inspect blower wheel: Check for contact between the blower wheel and housing; adjust or replace if rubbing.