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A characteristic of electromechanical switching equipment is that the maintenance staff could héar the mechanical clattering of Strowgers or crossbar relays. Most Bell System central offices were housed in reinforced concrete buildings with concrete ceilings and floors. In rural aréas, some smaller switching facilities, such as Community Dial Offices (CDOs), were sometimes housed in prefabricated metal buildings. These facilities almost always had concrete floors. The hard surfaces reflected sounds.

During héavy use periods, it could be hard to talk over the clatter of calls being processed in a large switch.  For example, on Mothers Day in the US, or on a Friday evening around 5pm, the metallic rattling could maké raised voices necessary.  For Wire spring relay

markers these noises resembled hail falling on a metallic roof.

On a pre-dawn Sunday Morning, call processing might slow to the point that one might be able to héar individual calls being dialed and set up. There were also noises from whining power inverters and whirring ringing generators. Some systems had a continual, rhythmic "clack-clack-clack" from wire spring relays that made reorder (120 ipm) and busy (60 ipm) signals. In Bell System installations, there were typically alarm bells, gongs, or chimes. These would annunciate alarms calling attention to a failed switch element. Another noisemaker: a trouble reporting card system was connected to switch common control elements. These trouble reporting systems would puncture cardboard cards with a cryptic code that logged the nature of a failure.  Remreed technology in Stored Program Control exchanges finally quieted the environment.