Furnace repair. The customer mentioned a loud noise coming from the furnace. After diagnosing and performing plenty of tests, found 2nd floor duct blade damper doesn’t fully open to the vertical position, causing the air pressure difference as the air goes around the damper, causing the noise. After manually opening it all the way and testing, the damper still opens to the “almost all the way open position,” however, the high-pitched noise has now stopped. Tested the furnace system multiple times. Giving a customer estimate for replacing the blade damper. What they have now they no longer make.