Good Fats, Rattling Sounds

I am not a pro in avocados.
So when I went to pick one up at a grocery store I found several fruit making a rather funny rattling sound with their seeds inside. I took a rattling one. It seemed to be ripe and ok. But the taste was a bit strange when I tried it. Should I have chosen a non rattling one instead?

A friend of mine told me I should just buy darker skinned avocados. So now I am after them. I want those healthy fats, yum