In the present work, the defect detection while using Discrete Wavelet Transform in rectangular plate structures is investigated. The plate bending is described by using the Boundary ElementMethod with boundary integral equations formulated in a modified simplified approach. The boundary elements of a constant type in a non-singular approach are implemented. Defects are introduced by additional edges forming slots or holes in relation to the basic plate domain. Estimation of the defect position is performed while using wavelet coefficients of curvature and deformation signals as well as a newly proposed moving variance estimator.