Effects of mean flow on the response and radiation of a fluid-loaded elastic structure have often been ignored as being equivalent to Doppler effects on frequency and amplitude, negligible at low Mach number. Mean flow effects are, however, generally much more significant than this, and can profoundly change the whole flow of energy into and through the structure-fluid complex. This paper will illustrate these effects in the context of the response of an elastic plate to single-frequency localized drive in the presence of uniform inviscid flow. For an infinite plate, the response typically consists of exponentially amplifying instability waves down-stream of the drive and two different neutral waves upstream; the drive point admittance generally has negative real part, implying energy flow into the structure and the drive, from the fluid. Approximations for various different parameter regimes will be given to predict these features. Extensions to semi-infinite and finite structures will be outlined together with interpretations in terms of negative-energy waves, and a discussion of viscous boundary layer effects. [Work supported by ONR.]