I reckon it is more to do with the NIMBYs who do not want any noise near them.
The noise monitors are placed in the most vocal areas and any deviation, whether for weather or traffic, is noted and reported.
Same deal in Australia, merely the noise monitoring people issuing a cop out statement to appease the public..
Just saw your ML locale. Check out ASA website for the monitors around Tulla etc for an idea. I am pretty sure the monitors are listed either there or on the DOTARS site.