Why does the Apache create much more rotor noise than the A-129?
Because they are very different helicopters, as egid already pointed out.


The Apache is twice as heavy as the Mangusta (5165 kg vs 2530 kg empty)
The rotor diameter is also bigger accordingly (14.6 m vs 11.9 m)


A Chinook transport will make more noise than an Apache. An Apache will make more noise than a Mangusta. Different helicopters and different weights that have to be kept airborne.