noise while flushing toilet

My son did not like to flush the toilet at night. Because his room is closed to bathroom. Flushing make a lot of the noise. Do you know what reason ?

Thanks.

because that is the way THAT toilet works. There can be many reasons why one toilet makes more noise than another one, but it is in the construction and design of the toilet, but also possibly a noisy fill valve, it depends on what the noise is.

http://science.discovery.com/videos/deconstructed-toilet-flushing.html

Thanks. Then it need more attention to nail that down.