Why does my song sound like it's all mush?

Hello,

I've been producing beats for about three years now. I started singing about a year ago, and in principle, my songs would sound good, but they don't. (1) I noticed that when I play my songs in the car, the whole song sounds like mush, and my voice is inaudible because there's no clarity, and you can't even understand the words.
(2) I noticed: when I don't listen to it in the car, but at home on my iPhone speakers (at 100%), then whenever the hi-hats are played there is always a background noise that is not nice and that is not present in other songs, such as songs by Yeat.

My question is whether ((1) and (2)) might be related, and I'm asking everyone for a possible solution. I'll try all the solutions mentioned and report back whether it works or not.

Thank you in advance!