Typically noise in a system is pressure related. The first thing to check is if the water source valve is completely open. If the spigot or faucet is only partially open this could be causing an issue with the pressure regulator, as it requires a certain amount of pressure and flow through the inlet in order to operate.
You may need to check your water pressure, this can be done using a simple pressure gauge fitted with the hose thread adapter to check the pressure, here is a link to our selection of Pressure Gauges. Then you also may want to double check the pressure limits on the items within the system, to ensure there are no items that have exceeded their pressure limitations.
If after checking the spigot is open, the items or the system have not been overtaxed, you will want to move onto the process of elimination. Before replacing any items, each head assembly component can be removed one at a time to find the cause of the noise.
To start, try removing the back flow preventer and run the system. If the noise continues, replace the back flow preventer and remove the filter, then the pressure regulator, and so on, until the noise stops. This may help to determine exactly which item is causing the issue.