How do I stop my double glazed window from whistling ?

Some advice please - I have double glazed windows fitted in my bedroom and they whistle. It seems to be only when the wind blows in a certain direction but it wakes me at night and is a dreadful nuisance. I have tried to find out where the whistle is coming from by taping up gaps/indentations one at a time but the problem has never gone away. Any ideas where the whistling may be coming from or how I could stop it ? Grateful for your thoughts.