Supposedly quite a lot of cars use some extra insulation on the wheel side of the wheelarch. I have heard of sound isolation kits for the Accord and Mazda 6, which supposedly do help a lot.
I too think that using some cloth there will probably keep the area damp and therefore prone to rusting - this problem is obviously more serious with Fords and their poor paint quality (last Mondeo's and Focuses had some rust issues).
However, there are some special materials that can be used instead of nylon - such as spray bitumen mixtures or brush-on bitumen.
To do this, you would have to remove the plastic liner inside the wheelarches and thoroughly clean the surface and then just apply a few layers on the metal area. This should have a great effect on road noise but it will also be protective against rust and stones chipping and denting the wheelarches. The original liner should go back afterwards, obviously.
I will probably do this all sometime later, at the moment I am looking forward to installing a sub and better rear speakers.
But for now, I am off to WRC Rally Deutschland and Prague in my car.
Got a cruise control installed for 500 euros and am really looking forward to meeting the autobahns
