Glueing outdoor carpet inside the roof. This is a quick way to get a nice finish inside the car, without the expense or hassle of a new headliner. It absorbs some sound, though glueing in a heavy layer of some padding before glueing in the carpet would have been good. Wear gloves when spreading the mastic. Even though it says "soap and water cleanup", it means that before it comes in contact with air. This stuff was pretty tricky to clean off anything after 5 minutes.
Here is a shot of the front of the passenger compartment with the mastic in place. This is a low VOC product for outdoor carpet from Lowes. Worked well. Let it set up longer than usual - maybe 15 minutes. This is really a two person job. Before the mastic, cut and fit the carpet so it extents behind the headliner rails. Make sure you mark the front.