When we turn on the washing machine, flush the toilet, do the dishes or take a shower there is a loud whistling noise afterwards that is very annoying? We are living in a new house an don't know what that noise is. Is is easy to diagnose?

Is the wistling nois during the usage of the washing machine, dish washer, and toilet or right after, and if you can clearify at what area you hear the sound, it looks like you may have a leak in the drian pipes.

Open and close your main water line from the city. Does shutting this valve down partially make the pitch change? I think you could have some sand or grit in the valve.