Oh dear, that sounds annoying. Resonator takes the edge off a bit and makes it slightly more refined, though it's still loud compared to standard. Luckily I don't use the motorway that much. Sometimes you can find a speed where it will get quiet(er), but might be well above 70.
2005 Fiesta ST
Milltek non-res, Newman fast road cams, Fusion Fabs custom inlet manifold