AA's 772s are all between 12-19 years old. They do tend to be a little louder in the cabin, but I don't notice it as much with the Bose NC headphones on.

It's possible you were on a newer 737 after that flight... and some of them are pretty quiet at cruise.

I just flew the E175 for the first time in F last week, and was very impressed with how quiet it is.