A dry-type transformer can make noise for several reasons, including:
Mechanical vibrations: when the transformer is in operation, the electric currents which pass through its coils can cause mechanical vibrations, which propagate in the air in the form of noise.
Resonance: if the transformer is powered by an alternating current source that oscillates at a frequency close to the resonant frequency of the transformer, resonance can occur which produces a characteristic noise.
Heat dissipation: dry-type transformers are designed to dissipate heat efficiently, but if the heat dissipation is not done properly, the internal parts of the transformer can overheat and generate noise.
Manufacturing defects: if the transformer has not been built with care or if it has been damaged during transport or installation, it may emit noise due to internal defects or short circuits.
In general, the noise produced by a dry transformer should not be too loud or intrusive. If the noise is excessive or occurs suddenly, the condition of the machine should be checked by a qualified technician and any problems corrected.
It is generally believed that dry-type transformers produce less noise than oil-filled ones, because as they do not contain oil there are no vibrations or liquid turbulences that could cause noise.
Additionally, dry-type transformers are typically designed to have higher energy efficiency and high-quality insulating components, which help reduce noise. However, the latter also depends on the transformer specifications and its application, as some dry-type transformers can still produce noise due to phenomena such as magnetic hum or vibration of moving parts.