Use of a VSD (variable speed device) on extractor fans can be very beneficial. If a fan is reduced 20% in speed it can quite often reduce power consumption by 50% and noise by an discernible level (not sure how much precisely). These are not that expensive to install.
An even fancier option is a smarter VSD that runs at 80% from say 6am to 10pm when people will be using their bathooms and then drops the power to 50% from 10pm to 6am. This would really get the noise down.
The cost of implementing the VSDs can be recouped in running cost savings over a few years. So no reason for an OC to not be keen to implement.