A diffuser, grille, or duct opening is whistling after startup. What should I check?
Treat whistling as an airflow/noise symptom. Check sharp edges, closed dampers, tight transitions, blocked path, kinked flex, wrong diffuser, loose grille, or air being forced through too small an opening.
Find the exact noise source and check face fit, flex/branch restrictions, damper condition, and sharp transitions before changing anything.
Do not bend blades, remove parts, or open/close balancing dampers randomly to silence noise.
Check
Exact device/opening
Loose grille/diffuser face
Kinked flex or crushed liner
Damper too closed or blocked path
Sharp transition/tap location
Steps
Locate the exact whistling device/opening.
Check if the noise changes when the grille/diffuser face is touched or seated correctly.
Look for kinked flex, crushed liner, sharp tap, closed damper, or blocked branch.
Photograph the device, branch, and any visible restriction.
Ask before modifying the opening, damper, neck, or controls.
Say this to your foreman
This device at [room/tag] is whistling after startup. I checked the face, flex/branch, and visible damper condition. Do you want me to hold for TAB, inspect upstream, or correct a visible restriction?