A cable-TV-based network transmits data on relatively high-radio frequency signals from a head end toward clients and transmits data on relatively low radio frequency signals from clients to head end. Radio frequency switch assemblies are distributed hierarchically from head end descending toward the clients. Each radio frequency switch assembly splits a descending path into plural branches, and includes switch units for alternatively blocking or passing low frequency signals from ascending the branches. When low frequency noise is detected at the head end, a noise source is located employing a test protocol in which switch units are sequentially set to block upstream signals, with the head end noise detector determining the effect of each switch disposition. Other types of hierarchical networks use analogous diagnostic methods.