We have studied YBa2Cu3O7-x ceramic samples during current cycling at 77 K using an acoustic emission method. We have observed the acoustic emission impulses at a narrow region current value of ±0.5 A. These impulses are reasoned to be the flux-line motion penetration into the samples by the magnetic self-field. Based on an experimental current value and the size of the sample, this H1 self-field value has been calculated to be 104 Oe. It is shown that the flux-line pinning process takes place most intensively in the narrow surface layer of a material.