This report summarizes the results of the KAPRI project, noise generation mechanisms of the percussive rock drilling and breaking hammer operations. At first, a literature study was conducted to find out existing knowledge on the topic. The literature study was mainly focused on the stress wave analysis and modeling of drilling equipment. Based on the findings of the literature study a brief theoretical introduction was written. The theory was tested in practice by conducting a series of strain wave, acoustic, and surface vibrations measurements under laboratory conditions. To gain more understanding on the vibration phenomena in drill steels computational models were developed to provide tools for the sound production modeling of the drill steels. The modeling approach was to utilize modeling techniques that have previously been used in musical instrument modeling, such as digital waveguides and dispersion filters. The modeling process was divided to two main approaches namely a longitudinal stress wave model and a transversal stress wave model that is used in modeling of the majority of the sound output generated in drilling. The research work in the project had also a separate minor research topic namely acoustical analysis of excavated tunnels in rock. Main results of the KAPRI include a literature study that covers the most essential content on the topic. A set of laboratory measurement data was collected and analyzed during the project. Digital waveguides were found out useful in the longitudinal stress wave modeling. The transversal stress waves can be modeled to some extent by using the FIR based approach. Preliminary steps in the acoustical analysis of the excavated tunnels were conducted.