[1PorscheBoxster986]

How is the airflow when changing fan speeds with the accordion ductwork removed as I suggested? This ductwork connects the air flow from the center console to your driver side vent.

I would remove the cabin air filter to see if that's the cause if you didn't have this issue before.

https://rennlist.com/forums/attachments/boxster-and-boxster-s-986-forum/378688d1250375962-sprint-booster-install-on-a-986-air-duct-removal.jpg
https://rennlist.com/forums/attachments/boxster-and-boxster-s-986-forum/378696d1250376146-sprint-booster-install-on-a-986-approximate-location-copy.jpg