Power transformers emit a very characteristic harmonic sound during operation. The sound spectrum consists of the harmonics of double frequency of the power grid with the fundamental of 100Hz or 120Hz in different countries around the world. This fundamental frequency dominates in the sound spectrum during the load condition while the higher harmonics are representative for the no-load operating state. Regardless of loading conditions, all the harmonics build rather unpleasant noise, which is difficult to suppress. Moreover, this noise is sometimes difficult to measure and interpret, due to the harmonic nature and a content of harmonics of relatively low frequencies.This paper presents the exemplary study on the assessment of noise damping efficiency, performed with the use of laser vibrometry and sound intensity measurements, which can provide the most complete information, when it comes to the identification of the sources of noise as well as to the proper evaluation of damping solutions.