You cannot compare the noise of a 250 to the 400. The 250, is much noiser and makes a very loud tinny noise which comes from the heat fins (air cooled). The 400 being water cooled does not have this noise. The sound from the exhaust on the 2 machines are similar.

 

it is odd but true the 400 is quieter than the 250. It is also way smoother and way more powerful. I love the 400 motor. I did not find the 250 Xplorer I owned to be that loud though, no were near a motorcross bike such as a CR 125. But it was a great machine.