It is not the smoothness of the road that is the main factor for road noise - it is the porosity of the surface.
The tarmac surface layer now in common use in Europe and the UK for A roads and Motorways was originally developed to minimise surface water retention and thus reduce the risk of aquaplaning. It is very porous. It was unpredicted that this would result in a quieter ride with most types of tyres.
This is because the amount of air trapped in the contact area was significantly reduced - the trapped air had somewhere to escape through the porous tarmac rather than be ejected sideways at the surface which resulted in a roaring sound.
On the subject of grit dressed roads - it is the case that when first laid they have greater grip than smooth tarmac - but the grit eventually wears to a highly polished and smooth surface which reduces the overall coefficient of friction with rubber tyres.
Hence both arguments are true
Newly gritted surfaces have a higher coefficient of friction than smooth tarmac - but this is soon lost when the protruding grit is worn down to a smooth surface. Gritted surfaces, new or worn, are always noisier than the modern porous tarmac.
Smooth porous tarmac has a slightly lower coefficient of friction, but this remains almost constant for the life of the surface. Hence porous tarmac roads , compared with gritted roads, have less noise and a higher coefficient of friction (on average) over the life of each surface.
Gritted roads using unprocessed tarmac and rock chippings are much cheaper than porous tarmac and have a longer life - hence their continuing use in the UK on roads with a speed limit of less than 60 mph (95 kph) where aquaplaning is not considered to be a serious factor.
And there I rest my case m'Lord
