200Hz seems a low enough frequency (1.7m wavelength) that they could do active noise cancellation with a small onboard speaker designed to generate a similar so

200Hz seems a low enough frequency (1.7m wavelength) that they could do active noise cancellation with a small onboard speaker designed to generate a similar sound 180 deg out of phase such that it cancels in far field. Would probably need some DSP to generate anti harmonics as well assuming there are some nonlinearities.