David Crighton was struck down by cancer in his fifty-eighth year. He was then at the height of his career and was one of the most admired personalities in fluid mechanics. He had specialized in wave theory, helping to understand and solve problems of practical importance using the full power of mathematical method. Efforts to control the sound and vibration caused by unsteady flow were never far from his thinking, and Crighton's contribution to those efforts has changed significantly the way the subject is viewed. Having first attracted him into the field and never losing my interest in the way he was influencing it, it is natural that I should comment on the technical developments while looking back on Crighton's professional life. The subject has changed a great deal and there are now many more researchers involved in its study, many of whom rely on techniques that Crighton pioneered – really powerful mathematical methods. But the basic problems remain: powerful flows are noisy.