night time song puzzling me

[wildben]

i live in a wood in east sussex, i hear a repetitive noise all night and in the day and can think of no other explaination than some bird
it sounds like someone blowing a whistle but not quite as sharp and it gets right into your head and is a bit uncomfortable,it makes the ear peircing whistle for 1 second then a 2 second pause then the next tone the pitch drops then it gets higher then stops ....