A hearing aid is disclosed, having the ability to generate its own open-loop feedback scan of amplitude (as gain or attenuation) and phase, as a function of frequency. The hearing aid has a sensor that receives ambient sound from near a patient, and a driver that stimulates the anatomy of the patient. The hearing aid has an operational mode in which the driver stimulates the anatomy of the patient in response to the sound received at the sensor. The hearing aid has a test mode in which a test frequency is stepped through a predetermined range of frequencies. At each test frequency, the driver is driven with a sinusoidal driver signal at the test frequency, the sensor detects a sinusoidal sensor signal at the test frequency, and a comparison of the sensor signal to the driver signal produces an amplitude (gain or attenuation) and a phase for the test frequency.