A project I worked on suggests vibrating the bone just under the earlobe at around 50kHz with a piezoelectric stack might help. 8 years or so ago I helped make a pocket sized and rechargeable medical device that operates on this principle. Last I checked it was still in FDA hell but helping the majority of sufferers in the trials. The theory of operation is that is breaks up tiny air bubbles stuck to the hairs in the inner ear.
An interesting side note is that you could 'hear' a very high pitched sound when using the device even though 50kHz is far outside the standard human hearing range. We still are not sure but think we were hearing a lower harmonic of the tone bouncing around the skull.
I wonder if you are hearing a "beat" tone (a third tone which is heard when two tones of different frequency are played. Playing tones at 500 and 600 Hz will also cause a tone at 100 Hz to be heard). This is how 3D positional audio systems work -- they beam two ultrasonic tones, and the difference tone appears to emanate from where the ultrasonic beams intersect.
Sending 50kHz vibrations into the earn should interact with a 49kHz tone to cause the listener to hear a 1kHz tone.
(This is all from an acoustics course I took over a decade ago, so take it with a grain of salt!)
An interesting side note is that you could 'hear' a very high pitched sound when using the device even though 50kHz is far outside the standard human hearing range. We still are not sure but think we were hearing a lower harmonic of the tone bouncing around the skull.