The present investigation is concerned with the sound‐production mechanism of primary small plate tones (S1 tones) generated by the impingement of a choked jet on normal flat plates with a diameter equal to the nozzle exit diameter. The power spectra associated with S1 tones typically contain a fundamental tone and many harmonics. These tones occur when the plate is located in a particular region of the jet. Photographic evidence indicates that S1 tones occur when a Mach disk cuts off a portion of the first conical shock wave leaving a frustum and a standoff shock wave forms in front of the plate. Timed schlieren photographs indicate that sound is generated when the jet boundary near the standoff shock wave contracts suddenly. This occurs as the first shock wave moves downstream and begins to interact with the standoff shock wave. The resulting sound appears to be somewhat impulsive. Reflector tests indicate that the tones may not be part of a feedback loop to the nozzle. Simplified calculations show that once the first shock wave is set into motion, its continued movement downstream is due to an increase in the compression of the upstream fluid.