Could you give us tips on how Americans can be respectful when visiting China? for example: I noticed most of us Americans talk really loud compared to people from other countries. What is polite in a restaurant, on the train, etc. What are the pet peeves that people of China have regarding Americans. How do we leave a good impression?

I think you don't need to do something painstakingly,just be yourself and act it naturally. Anyone who comes to China is our friend and we are doomed to spend a pleasant time with each other. Take it easy and enjoy yourself in your China travel.
Welcome you to our country,dear friend!

After all China is a developing or developed country. Tourists are the guests of the country who are contributing in the State revenue. As such Americans will be honored and respected with all amenities and securities in China- one should not doubt about it to down grade the prestige of a country.