Take it down to the weigh bridge and get it weighed. You need the front and rear axle weights. It needs weighing with all your normal stuff in it including passengers, fuel and water. Then you can work out the optimum tyre pressures for the axle weights and then let the tires down. If it's come from a Dealer they are probably 80 PSI all round.
If that doesn't work sell it and buy something with better sound proofing