You usually get a whining noise when there is too little pressure, i.e., when a valve isn't open enough. And it goes away, when the pressure is increased, i.e., when the valve is fully open.
The clunking when you first open a valve may be due to a pipe not being secured properly. Perhaps it has recently come loose and that is why you now hear the noise.
The backflow preventers just screw on to the hose bibb and you screw the hose onto the backflow preventer, so there's not much you can do wrong there.