I dont know of an issur but there is an issue that nobody mentioned.
I remember hearing that the Nazis used to whistle specifically Mengele yimach shemo vezichro may he never leave gehennom used to whistle and act in a very care free relaxed attitude while making his selektion of who goes where. That is why many holocaust survivors are anti whistling and find it repulsive. This likely seeped down to their children and they got the idea that whistling is bad but not necessarily with the why so many assume it is halachic but it isnt a halacha to my knowledge.