I've just thought of something.
A lot of people tend to wear ear phones listening to music in the street, I wonder if Aliens know that certain people are on to them and some do this to drown out the potential of these whistles or even maybe better whistles of frequencies that someone could have found to work.

What I stumbled upon was pure luck but maybe more people know about this.
Ok , I could equally be barking up the wrong tree like I said earlier, yet if we don;t try, we will never know, will we.