Landed outdoor unit rattling: storm-bent fan guard tab touching the blade

A Serangoon landed outdoor unit started rattling after a storm passed through. The sound was loud enough to suggest a mechanical fault, but the garden setting mattered. A branch strike during strong wind can bend guard hardware without the motor or compressor being at fault.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Mitsubishi Heavy Industries Wall-mounted9 years oldLandedSerangoon, Singapore

Concern: The rattle sounded harsh enough that the owner suspected the outdoor fan motor or compressor.
Found: A wind-driven branch bent one fan guard mounting tab inward, letting it touch the spinning blade tip
Key check: Checked the fan guard's mounting tabs and blade clearance before quoting parts
Result: The rattle stopped once the tab was bent back clear of the blade. The unit cooled normally, and the owner had a simple inspection point for future noise after any storm strong enough to strike branches against the unit.

What we were told

The living-room aircon cooled, but the outdoor unit started making a sharp rattling sound after a storm blew through the garden. Night use paused because the noise carried across the garden and sounded like something was breaking. There was no cooling complaint yet, so the sound pattern and weather timing mattered more than temperature.

What we checked

Because cooling had not collapsed, we did not begin with compressor assumptions. We asked when the noise started, then inspected the fan guard and its mounting tabs facing the garden. The guard, blade clearance, and mounting points were checked before any part quote was discussed.

The unit still cooled and started normally.
The rattle changed as the fan speed changed.
One fan guard mounting tab was bent slightly inward.
The mounting feet were firm, but the bent tab lightly touched the blade tip at speed.

What we found

A branch had struck the fan guard during the storm and bent one of its mounting tabs slightly inward. At running speed, that tab now sat close enough to the fan path to make intermittent contact with the spinning blade tip, producing a loud, uneven rattle that sounded more serious than it was. The timing right after the storm and the garden-facing placement made a wind-driven strike more likely than a failing compressor. The motor was still starting normally, and the unit still cooled, so a major part quote was not supported by the checks.

What fixed it

We bent the mounting tab back clear of the blade path, then confirmed even clearance around the full blade sweep before running the system through several starts. We also checked the remaining guard tabs and mounting points for similar storm damage. If the rattle returned without contact at the tab, then motor and mounting checks would come next. For this visit, the fix was a guard adjustment, not parts. The owner was also shown where overhanging branches sat closest to the unit, since that side is most exposed in strong wind.

Outcome

The rattle stopped once the tab was bent back clear of the blade. The unit cooled normally, and the owner had a simple inspection point for future noise after any storm strong enough to strike branches against the unit.

What this case teaches us

A storm-bent guard can sound like a major outdoor fault

A sudden rattle right after a storm should make us check the fan guard's mounting tabs and blade clearance first.
Landed outdoor units sit closer to overhanging branches than most HDB ledge units, so a wind-driven branch strike is a realistic cause of bent guard hardware.
Send a short sound clip. If the noise is irregular and started right after a storm, a bent guard tab is a realistic first check before parts.

Questions this case answers

Outdoor unit started rattling right after a storm: what should be checked?

The fan guard and the blade clearance. On this Serangoon garden unit one guard mounting tab had been bent slightly inward, close enough to make intermittent contact with the blade tip at running speed. The rattle changed as fan speed changed, and the mounting feet themselves were firm.

The noise sounds harsh, so is the fan motor or compressor breaking?

Harshness is misleading. Intermittent metal contact makes an uneven, alarming sound while the motor underneath starts normally and the unit keeps cooling, which was exactly the picture here. Bending the tab back clear of the blade path and confirming even clearance around the full sweep ended it, with no parts involved.

Are garden-side outdoor units more exposed than ones on an HDB ledge?

To wind-driven debris, yes. Landed units often sit under or beside overhanging branches, so a strong storm can drive a branch into the guard hardware without anyone seeing it happen. The owner was shown which side of the unit the nearest branches overhang, since that face takes the impact.

What is worth sending before someone attends a noisy outdoor unit?

A short sound clip, plus when the noise started. An irregular rattle that began immediately after a storm reads very differently from one that crept in over months, and it puts guard hardware ahead of parts in the checking order. Cooling status matters too: still cooling narrows things considerably.

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Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.

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