One motor's vibration is getting through the gyro filters

What ArduPilot says:

• Noise %.fdB on motor N at %.fHz

This check is one you switched on: the gyro FFT (FFT_ENABLE 1) looking at the signal after the filters, with FFT_OPTIONS bits 0 and 1 set. In flight it takes each motor's rotation frequency from the ESC telemetry and measures how much of that frequency is left in the filtered gyro signal. For the motor named, more than 40 dB is left: its vibration reaches the attitude controller. At most one report every 5 seconds.

What to do, most likely first

1. The harmonic notch filter does not follow the motors.

   FixSet the notch to track ESC telemetry: INS_HNTCH_ENABLE 1, INS_HNTCH_MODE 3, and in INS_HNTCH_OPTS bit 1 for one notch per motor. Reboot and fly again.

2. That one motor vibrates more than the others: a chipped or unbalanced prop, a loose mount, a worn bearing.

   CheckThe message always names the same motor.

   FixChange the prop, tighten the motor, and compare the motors on the bench (props off unless the aircraft is tied down).

Parameters to look at

Where to do it:Setup & Tuning GuideStarting Parameters