Hi blokespeed ,
living in China so far I did not have any problem with my neighbours , but last time when I've moved to my new appartment , one lady from upsters came once in the morning , I was just waking up so my hairs and the face had to be very horrible , in fact when I've opened the door the lady at first was kind of shocking , then she asked me if I could play not too late during night time , I've said ok , but honestly I still play sometime during night , and the lady never came back to complain !!! I think she's a bit afraid of me , she will always rember how afraid she was that time when I've opened the door , you should know that I'm 1.90 m high and have long hairs and beard sometime , so for a chinese a man like me can make them run away !!!
Anyway I must tell you that during night time I'm a bit carefull with what I play with , mostly during night I play a kalimba , or a tin whistle muted with some foam , or a very low key shakuhachi , so they are not very noisy !
So the best is that you mute the whistle , in any of the ways people suggest you , or try a very low in sound instrument , or just do as I did ; if you don't have long hairs or beard just buy a wig and a fake beard and get an expression like Jack Nicholson's eyes in Shining !!!
All the best
Manuel