Another problem with vibration entering the wall framing is that your ceiling and floor are connected to this same wall. So his sound is also entering your room through your floor and ceiling. This is known as flanking noise. Not as much sound will come through the floor and ceiling, but perhaps 30% as much as the wall, and you’re hearing it in stereo.
Solutions for Soundproofing your walls
We would prefer to treat the wall from his side to immediately destroy the vibration before it gets into your wall framing. This is generally not possible, and he probably doesn’t want to help you anyway. So really all you can do is treat the wall on your side..
Option 1 – Add drywall and Green Glue
Add two layers of standard 5/8” drywall and Green Glue. Make the wall as heavy as possible with standard $8 drywall. Install a medium coverage of Green Glue between the layers. This will reduce a great deal of the vibration, but certainly not all, since the vibration is racing through the wall framing behind the new drywall layer.
Option 2 – Remove drywall & add Sound Isolation Clips to the wall framing members
Remove your existing wall drywall and install standard R13 fiberglass (nothing thicker or expensive).
Then install the less expensive decoupling clips and channel. This will reduce the physical contact points when you add your new drywall and quite effectively decouple your new drywall from that original wall framing. Then double drywall and Green Glue. This solution utilizes all 4 Elements of Soundproofing.