My car's had the back boxes cleared out by the previous owner. It's pretty loud at idle or when accelerating, but you don't notice it while cruising at a steady speed because at 50 km/h it's not significantly above tire noise anymore, and at 90 km/h you only really hear tire and wind noise, no exhaust.

Now if you cut out the resonators, that might cause significant highway drone that would be annoying as hell.