Apprentice question
Field check
Standard work. Do it right, keep moving.
Large thin-wall round duct can resonate. Check vibration source first, then add approved acoustic isolation, wrap, or stiffening.
['A big spiral barrel can behave like a drum skin when fan rumble, vibration, or pulsing air hits it. The fix is not always inside the duct.', 'Check equipment isolation, flexible connectors, supports, and whether the duct skin needs external acoustic wrap, damping layer, stiffening rings, or a silencer/detail change.']