Duct is rattling or vibrating after startup. What should I check?

Stay clear and treat it as a support/connection/isolation symptom. Check loose hangers, long unsupported spans, rubbing against structure, stretched flex connectors, loose joints, and equipment vibration transfer.

Find the source and check supports, joints, flex connector, rubbing, and equipment vibration before adding random fixes.

Airflow, Noise, Vibration & TAB 2nd Year YELLOW

Watch out

Do not grab vibrating duct, wedge scraps into hangers, or silence the noise without finding the cause.

Check

Where vibration starts
Loose support or joint
Metal touching structure
Flex connector stretched/tight
Equipment isolation/fan connection

Steps

Stand clear of moving/vibrating parts.
Find where the vibration starts.
Check supports, rods, trapeze, joints, flex connector, and equipment connection.
Look for metal-to-structure rubbing or loose parts.
Record a short video and ask before adding random screws, shims, or braces.

Say this to your foreman

After startup, this duct rattles/vibrates at [location]. I checked visible supports, joints, and flex connector. Do you want me to correct support, hold for TAB/startup, or inspect another point?