For one, I think it's important to point out that this forum is in no way affiliated with Amtrak. Most of your concerns would probably be much better addressed directly with Amtrak themselves.
That being said, let me offer some pure speculation. Assuming you are correct that Amtrak's horns are louder, the likely reason is that Amtrak travels much faster than freight railroads - typically 20 MPH or more faster. So trains need to be heard from a much longer distance away to provide the same amount of warning. Most people are expecting a freight train at a crossing and a number of fatalities occur each year when people try and beat the train, expecting a much slower freight.
If your community is concerned about train noise, consider trying to raise the funds to become a quiet zone. This involves putting in quad gates at all crossing across a minimum of five miles. But that would result in trains being able to pass through town without sounding their horns. And quad gates save lives by preventing people from driving around lowered gates. This is what we have in the south end of Burlington, where I work, and several freights pass by a day without ever touching their horns.
Working on a project such as that, rather than gathering db data, would have positive benefits for everyone involved.
