If you are wondering whether you should say that something sounds “good to your ear” or “good to your ears”, rest assured that either choice is fine (and, of course, the adjective does not have to be “good”). Nevertheless, if you want to be on the safe side, use the plural, which seems to be more common, e.g.
There are, however, a few idioms where the plural is not optional. The phrase “being in something up to one’s ears” means “being very busy or overwhelmed with something”, for example,
When you say that something is music to your ears, it means that it is exactly the thing you wanted to hear, e.g.
It can also mean that it is very pleasant or soothing, as in