What is it about the word you find ugly? Is it the sound? the meaning?

I had stated elsewhere that I found the word nacreous ugly, strictly from the sound of it. Murmur is another word that you will find on many people's most beautiful words list, but I find it a bit questionable; it contains, at least in my dialect, the [er] sound that they always warn us against in choral singing. Giving it the [ih]* sound they tell us to use instead only seems to make it worse.

So what is it about this word or any other that makes it ugly or beautiful?

* [ih] the sound I am trying to get at here is something between [ih] and [uh] and [eh]. Not quite sure how to describe it.