The influence of a turbulent air stream on the sound attenuation in ducts, lined with sound absorbing materials or structures of different kinds, has been experimentally investigated. For linings consisting either of porous materials or sufficiently damped Helmholtz resonators, decrease of absorption with increasing flow velocity has been observed, together with an increase of the frequency of maximum absorption in the case of the resonators. Somewhat surprising results have been obtained for undamped or weakly damped Helmholtz resonators, where an attenuation minimum is observed above the resonant frequency, the frequency of which increases linearly with increasing flow velocity, and which—for undamped resonators—even reaches negative attenuation values. Aside from the negative attenuation, a self‐excitation of the duct is observed under certain conditions, the frequency of which is not identical with the attenuation minimum.