1. My speakers sometime have this feint crackling sound (like a HDD working) at very low levels. It's barely audible, many people have this issue and I decided I don't really care as you have to put an effort to hear it. I hope Apple will fix it with some fw update, but even if they don't, it's fine.
2. After keeping the lid closed for a while, there is a slight (like really slight, barely noticeable) sticking sensation, but nothing like I had on previous MacBooks. It's really feint and if it doesn't get worse, I totally won't mind.
3. Finally, the keyboard leaves dust marks on the screen. They are not large, but in time they will become permanent (based on experience). I had this (and worse) on all of my MacBook Pros and they are never visible when the screen is turned on, so they don't bother me much.
I assume that I also have "backlight leaking" from some of the keys (some of them have thin lines of light when looked at an angle) but I had this on literally any keyboard with backlight that I ever used.... caring about this is beyond my understanding. If this bothers you, I don't know what to tell you. So I'm only mentioning this because I've seen people mention this. I don't even consider it an imperfection.
So, these things. I wouldn't bother replacing my Mac because of them even if it was hassle-free (if I lived in US, here it is more of a hassle) and I sometimes find it strange how people return several units because not everything is "perfect". The stress and waiting is not worth it. It doesn't have to be perfect, it needs to be reliable and work well. Nothing is perfect. If you think the cost entitles you to some unrealistic perfection, perhaps you're not actually comfortable with the price.