Internal sources of flow unsteadiness can contribute substantially to the airfield noise from jet engine exhausts. Since this noise contribution often takes an indirect path to the farfield observer, it is not always clear that the source is inside the duct and not in the jet, as a directional microphone might suggest. Direct cross correlations, between in‐duct and farfield microphones can be used to demonstrate the relationship between the source region and the observed signal. In addition to knowing that the two are related, it is of interest to know how much of the farfield noise is due to sources inside the duct. Experiments in which a source in the duct is driven by sine waves, narrow‐band noise, and broad‐band noise are used to demonstrate the use of the normalized cross correlation to show a quantitative relationship between the source region and observer. Aerodynamic sources are added and the method of determining their relative importance is discussed. The technique is then applied to the evaluation of the contribution to overall exhaust noise made by unsteady combustion and/or flow over struts inside an engine. [Supported by NASA Grant NGR 31‐001‐241.]