On my 110 TD5 SW l fitted under bonnet insulation pads, plus some sound deadening mat under the seats and under the second row seats where you can see bare metal.
lt's got carpet fitted throughout as standard, and rubber mats in the foot wells/rear load area.
Sound levels are around 80db at 65mph. l am not sure you can expect much better, the Defender is about as aerodynamic as the factory it was made in.
l tried coasting at 65mph (engine idling) and noise levels barely changed. So it's not the engine.
One thing that did make a difference, was sealing the bonnet/bulkhead with self adhesive D-seal.
This made a difference of around 2db in the cabin, it doesn't sound much but it was noticeable.
Also you can now open the vent flaps at lower speeds and noise levels inside don't increase at all.
