It means something sounds really nice to some people but not so much to others.
Like,
"Ben Shapiro's rhetoric against liberalism is music to some people but noise to others."
It means some people love Ben Shapiro's views on liberalism but some others hate his views.

Are we talking about porn? Because some people are hypocrite

理解成“萝卜青菜，各有所爱”？

句子不正确，楼上指出来了。
感觉这句话其实应该是：
What is music to some is noise to others; why？或者
Why does something sound like music to some and noise to others？或者（最简补全）
Why is it music to some ears and noise to others?
(请检查一下你是否抄录正确）。