I spoke to hydro and he blows air through his filter which stops the noise of air leaving the ducting but said its still louder than he would like where the air is going into the extraction fan, where most of us would have our filter.
This got me thinking about trying to have a new filter on the front of the extraction like normal and have a old filter on the end of the system. The only issue with this is it will greatly reduce the airflow. The fan pulling through and pushing through 2 filters.
I then looked at a old filter and though about removing the carbon. It would allow a lot more air through the filter carcass but should muffle thst really loud whoosh of the air leaving the system.
Ill do a video once it's set up to see if it works.