Almost everyone who's in a relationship has some things about their partner that annoy them. Even those who are head over heels will never be presented with the idealized version of their beloved 100% of the time. Still, it can sometimes be hard to tell what the ramifications are of that trait you don't like about a person. It could be a blip in a lifelong grand romantic narrative, or an indicator that it isn't actually going to work out.
This is part of what has encouraged the Zoomer slang phenomenon of the Ick: something a romantic interest does or says that quashes your affections. Sometimes they're major, but more often they come about from small, inconsequential things. They can be the source of much angst, and one anonymous woman's notes app list detailing those she has for "Joseph" has prompted a whole discussion about this.
Listing things like the fact that he sings in the car, many struggled to see what her issue was. Perhaps she's focusing on the wrong things, or trying to convince herself of feelings that aren't there.