Reliability and noise tolerance represent important requirements for electronic systems and in particular for networked systems, especially in critical working conditions. Reliability and noise tolerance mostly concern the communication tasks between the network nodes, which are implemented complying with formal protocol rules. The challenging target for a reliability analysis is to provide comprehensive evaluations and acceptably accurate results. However, the current complexity of the protocol and the complexity of the networks with many nodes make it very difficult to achieve this target. This paper presents a novel system-level methodology for noise analysis of digital networked systems. The methodology is based on a simulation and analytical approach capable to address a fast and comprehensive study of the reliability properties complying with the protocol specifications. As a test case, the MOST 150 protocol has been considered. MOST 150 protocol is currently widely used for multimedia networks in automotive applications.