M400 Cooling system noise

[T_Kris]

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M400 sound like a APU spooling down after landing, sounds like an overworking cooling fan. It’s been like this for the last week or so. Should I be concerned? Anyone have similar?

 

[Smittybombs]

Mine just started doing the same today. Upgraded firmware last week, brought it out to test it, and noticed a high pitch whine during flight and the same sort of sound after landing that you describe. Decided not to fly more until I investigate further.

 

[Smittybombs]

Prior to updating the firmware, I was on V16.00.0813 with the drone working fine and no loud sounds. I updated to V16.01.0809 and that is when the sound appeared.

Today, I downgraded back to V16.00.0813 and the sounds went away, no whining during flight and no loud post flight whirring.

Then I upgraded the firmware all the way to V17.00.0100 and both the in-flight whine and the post flight whirring returned. I tested it a lot, short and long flights, altitudes from 20ft to 400ft, DRTK3 and GNSS, no payload and H30T, and all three standard flight modes. The drone flew great, no issues, no warnings, and the health management system was green the entire time.

Both V16.00.0813 and V17.00.0100 enable features related to the new delivery and cleaning flight modes. These modes would increase hover time, meaning less passive airflow into the body. My guess is that DJI has increased fan speeds to help with cooling during flight.

I've reached out to my vendor support team, and they're checking with DJI. If I hear anything else I'll post it.