D-term noise
D-term noise is high-frequency noise amplified by the derivative (D) term — it drives the motors hot and can degrade tracking.
Because D is a derivative, it amplifies gyro noise; without adequate D-term lowpass filtering that noise reaches the motors. PIDoctor shows the D-term FFT spectrum, flags "D-term noise on {axis}" and recommends D-term lowpass / dynamic notch changes.