The internal-friction (IF) technique is applied to study high-T_c superconducting Bi-Sr-Ca-Cu-O (BSCCO) system cuprates. IF measurements at five different frequencies from 10^-2 to 5 Hz in a temperature range from room temperature to 330 degrees C are carried out. Resonance-type behaviour of IF at a very low frequency (10^-2 Hz) appears once the sample is slightly deformed ( in approximately=10^-4). The IF characteristic of the high-frequency side of the IF-frequency resonance peak is thus determined. It is suggested that the resonance originates from two-dimensional defect vibration, and most probably the domain wall motion caused by dislocation translation.