The paper presents the sources, the propagation paths, the vibration mode behaviours and the noise radiation properties that control the noise radiation in the front side of a diesel truck engine. Measurements and analyses of vibrations and radiated noise have revealed that the overall noise from the engine front radiates from the timing transmission casing, the oil sump front and the belt pulley/torsion damper arrangement. The transmission cover on the investigated engine is coupled directly to the oil sump front and it is manufactured in cast aluminium. The cover and the oil sump front show strong coupled modes that are dominant radiators of noise in the frequency range 630 Hz - 1 kHz. The noise from the transmission cover has been reduced by replacing the interior plate of the cover with plastic plates that have decreased radiation efficiency and increased damping. The radiation from the narrow opening between the torsion damper and the transmission cover was found to be an important radiator and to be caused both by the cover and the damper. A damping ring covering the opening was found to produce substantial reductions of noise.