There is no doubt that there is minimal insulation in the xp90. Its so bad, I though I was driving a scooter the day I bought the car. If you really want to eliminate foreign noises inside the cabin, you will have to spend at least 50k. To make the cabin as quite as possible, you need to do three layers of sound insulation/deadening.
1) Sound Deadening Sheets to reduce rattles and body flexing. This prevents any squeaks and metal resonance. This is a link to my vitz where I did all the doors, trunk, a,b,c pillars and front firewall. I also did parts of the floor.
2) Mass Loaded Vinyl. This is sound barrier. It prevents sound entering the cabin. Use these on the floor, trunk, firewall and wheel arches. You can use them on the inner sheet of the doors too. Here is picture of a mlv applied to a G-class wagon. I've bought the sheets for my vitz but havn't yet got the time to put them on.
3) Closed Cell Foam. These act as sound absorbers by muffling the sound. Most people in pakistan use Jumbolon since CCF is kinda hard to find here. Jumbolon works great aswell. It may not be a CCF to be exact but it works in a similar fashion.
The three of these combined will do wonders to the cabin noise levels.