In the absence of a nearby metal object, the two inductances LA and LB in a heterodyne metal detector are the same, and the resonant frequencies of the two oscillator circuits have the same value of 460 kHz. When the search coil (inductor B) is brought near a buried metal object, a beat frequency of 8.6 kHz is heard. By what percentage does the buried object reduce the inductance of the search coil?