Among cavity pumps used in hydraulic drive systems as energy generators, gear pumps are the most widespread. Apart from their numerous advantages from the point of view of noisiness and the delivery fluctuation coefficient, they are inferior to others. Steps are undertaken to decrease the noisiness. According to the research results, own acoustic parameters of the pump depend on the technology and performance quality as well as on the geometrical features of the tooth profile. The paper is restricted to the analysis of acoustic properties of an innovative gear unit after tooth root undercutting. Acoustic properties have been described with taking into consideration induction of decision trees and decision rules.