Water Hammer (noun)

\wa-tar \ham-mar\

An aggravating noise which may wake you at various times during the night and in the early mornings

Often inflicted by neighbours who lack the ability turn taps on and off with a gentle motion. Although not restricted to, will often be found in high density living situations where its affects can reach a wider audience

Not to be confused with the 'hammer' sound that is generated from the impact of a tool against a hard surface. The 'hammer' sound will most definitely be found in the wee hours of a Saturday morning.