Noisy Bird

My neighbours have recently acquired a bird without permission.  I haven’t seen it, but all day it makes a noise like someone blowing a whistle.  I have recently been home sick, trying to read and it is irritating.  Granted we live in an area that has a lot of birds, however, these birds make a noise and then go.  The neighbour’s bird makes this noise constantly when they are out and that is usually the whole day.  The residents (tenants) are not ‘approachable’ people.  Any ideas?