They are extremely loud, second only to no muffler cars and sport bikes blasting through deserted back roads.
If you live in the woods with trees, they'll sound as loud as the ocean. If you live near the ocean, well that's always loud.
The biggest offenders are:
1. cars/trucks 2. birds 3. airplanes 4. ac units 5. ocean 6. wind with trees
You'd never know trees sound like the ocean if you aren't around trees. Trains are loud but intermittent. And trains don't run very often anymore where I am.