2017 Outback Limited 2.5, Twilight Blue/Ivory, Eyesight. Also 1995 BMW 525i with 240,000 miles
I plan to soundproof my front doors next spring so I will "glue" as has been mentioned.My 2016 OB Limited drivers door is having the hollow sound now too. Going to try the silicone treatment myself as well.
Not sure it has been mentioned but some Outbacks, like mine, have the factory or dealer installed color-coded door protection strips. These will help stiffen the door skin a great deal.