A large TDC/Ductmate flange is whistling or leaking at startup
A whistling flange usually means the joint needs to be reopened or corrected, not just smeared from the outside. Check gasket, corners, clips/cleats, bolts, support, flange bowing, and approved seal method.
Do not just smear mastic over a bowed or bad-gasket flange and call it done.
Check
Listen/feel for the exact leak location without putting hands in unsafe airflow/equipment areas.
Check all four corners, gasket continuity, flange alignment, clips/cleats, bolts, and joint support.
Look for flange bowing or duct weight pulling the joint out of square.
Reopen the joint if the gasket is folded/missing instead of sealing over the problem.
Use the approved connector/seal method and retest or recheck before insulation/cover.
Steps
Listen/feel for the exact leak location without putting hands in unsafe airflow/equipment areas.
Check all four corners, gasket continuity, flange alignment, clips/cleats, bolts, and joint support.
Look for flange bowing or duct weight pulling the joint out of square.
Reopen the joint if the gasket is folded/missing instead of sealing over the problem.
Use the approved connector/seal method and retest or recheck before insulation/cover.
Say this to your foreman
The TDC/Ductmate joint at [location] is whistling/leaking at [corner/side]. I checked gasket, corners, clips, bolts, and support. Do you want me to reopen/re-gasket it or correct the clips/cleats and reseal per approved method?