It seems like newer vehicles like to add things that go from the engine bay and route it through the firewall and into the cabin for some odd reason. There could be many reasons, but some manufacturers feel as if these such things need to exist to help connect the driver to the vehicle. These things include sound generators that connect intake noise or blow off valve noise to the interior.
And if you own one of these vehicles and get annoyed, then don't worry because Mishimoto has released the Subaru Sound Generator Delete Kit which has been designed to eliminate engine noise in the vehicle cabin. This kit features a CNC machined aluminum plug that will plug the intake hose, and installation is simple taking around 10 minutes to install.