Any pipe will have a resonant frequency, just like an organ pipe, which will appear to amplify sound, and it will be a low frequency for a large long pipe. Anything moving in the pipe can cause resonance vibration, especially if there is a partial obstruction or mixing of flows from different directions. The only way to stop it would be to block the pipe, but that could cause other problems. A generally quiet area will not generate enough other noise to drown it.
Christopher Bell ● 2676d