Jet discharge noise is predicatable from standard formulae.
I recommend "Noise and Vibration Control" by Beranek.
Basically the noise generated depends on the mechanical stream power of the discharge which is essentially the same as velocity pressure. The amount of the energy which is converted to noise depends on the Mach number of the discharged stream and the spectrum of the noise depends on the diameter of the pipe. What you hear depends on where you are relative to the axis of the discharge and how far away you are.
There are silencer manufacturers who specialize in suppressing this noise.
If you have specifics of flow and tail pipe size, steam conditions etc., I can pass them to a colleague who does this day-to-day and get him to contact you independently. If you're interested drop me an email at flareman_xs@netzero.net.