Cavitation is a damaging phenomenon that occurs within and downstream of control valves under certain well-understood temperature, pressure and media velocity conditions. At its very worst, cavitation creates high noise levels along with vibration, pitting and erosion of valves and piping.
The noise may be annoying or severe enough to be a health threat. However, the noise is only a symptom of the underlying problem — the process conditions. These conditions also may cause flashing, i.e., formation of vapor bubbles in the media; it doesn't always lead to cavitation and poses less-severe erosive effects.