Laid noise insulation from Car Builders under the mats up front on the firewall and floor and in the rear. Just cut to size with scissors,  peel off the back and stick it down. 
Don't have a noise meter,  but it has definitely muffled the higher decibel sounds and made the floor softer. 
I used a waterproof single cell insulation designed for 4 WDs. I have also fitted a insulation sheet under the bonnet. 
If you're interested just search Car Builders. 
https://www.aulro.com/afvb/images/im...017/07/293.jpg