A lever ball valve is not a good way to reduce water flow rate/velocity and "throttling down" or chocking as your friend calls it will certainly introduce more noise via turbulence to the system (as you've discovered). A proper good old fashioned stopcock is adjustable without introducing the noise like ball valves do.
A full bore lever valve is a great thing for reducing obstruction and therefore increasing flow rates but that seems to be the opposite of what you want in your situation.
I would change the full bore lever valve for a stopcock and have a play with that. You can close it down and test performance at your outlets and only have it open as far as you need for adequate performance at point of use.
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Just to add, you can keep your lever ball valve and use it as an isolator and cut in a stopcock after it, or you can replace the lever ball valve with a stopcock entirely. Either way will give you better control.