You didn't say what year and model you were looking at. Things are relative, a cheaper built unit will ride rougher than a Super C on a diesel chassis. The same way a 87 Yugo will ride differently than a 2020 Mercedes. As a general rule however, most gas MH's either A or C will make a good deal of noise going down the road. Some rattles can be chased down and fixed (I was obsessed over this on our previous 2 class A gassers). Some noises would be a greater concern than others, depending on what is causing the noise. LOTS of contributing factors, tires, PSI, alignment, weight distribution, things not stowed properly - a million reasons. You'll need to drive quite a few to determine what's normal and acceptable vs what you can tolerate. If you want the best ride for an RV, look at a diesel pusher.