While it may be unlikely that the person who asked the question ten years ago is still around without having found an answer, ...

for most blown instruments, a difficulty for beginners is understanding how much effect the "back volume" formed by the mouth and throat can have on the pitch and tonal quality of the instrument.

Practice with making the "mouth pitch" match the pitch you want the whistle/flute to play does help a lot, and you can do that very quietly without even having the instrument at hand.

Just pucker up, with as close as you can get to the blowhole configuration you would use if the flute/whistle was there - call it by it's snob name of "forming your embouchure" if you like - and "blow the tune." Note that you're NOT attempting to "whistle." All you want is a fairly gently air stream that "fits the pitches" of a tune. Any sound you make can be nearly inaudible and still have a clearly defined pitch.

While performing this "practice" you should try to feel and be aware of what you're doing to "tune the airstream" that would be going to your instrument. Then try to do the same thing with the instrument in, or at, your mouth when you get to your real "practice place."

The better you get at matching your "head volume" to the pitch your instrument is playing, the better you'll be at playing at a variety of loudnesses with the instrument, and although you'll still make some noise when you add the instrument, with most instruments you should soon be able to "play it pretty" - and softly - enough to avoid drowning out the neighbors' yelping pups.

Most keyless instruments come with a little paper or booklet telling you "how to play the #@!% .... whatever," invariably telling you to "blow harder" to play the second octave. While for most such instruments there is a minimum pressure/velocity needed for forming a stable tone inside the instrument, with proper "back resonance" tuning inside your head you'll find you can flip between octaves/registers quite easily with nearly indiscernible change in how hard you need to blow: and you'll be able to do it at much lower - or when needed at much greater - loudness.

Pucker up and blow (gently) in tune, as if you had an instrument, and you needn't annoy anyone. It will help when you get back to a place where the noise of the instrument is acceptable.

John