  It is well known that an air flow in a corrugated pipe might excite the
longitudinal acoustic modes of the pipe. In this letter is reported experiments
where a low frequency, oscillating flow with velocity magnitudes of the same
order as the air flow has been added. Depending on the oscillation strength, it
might silence the pipe or move the resonances to higher harmonics. It is also
shown that a low frequency oscillation by itself might excite a higher
frequency acoustic resonance of the pipe.
