I started this thread as a potential Mazda 3 buyer. I'm now posting as a new owner of a facelift model Mazda 3 2.0 petrol sedan with Dunlop Sport Max TT tyres on 18" wheels. This is a UK model produced in Japan.
In terms of road noise, my opinion is that overall the car is relatively poor. The road noise is just about acceptable on a smooth road but it then degenerates quite markedly as soon as you drive on a rougher surface. I'm also surprised how loud raindrops falling on the roof and windscreen sound.
I dislike the unpleasant 'throaty' engine noise when starting the car in my garage. I understand this is due to Mazda's accelerated warm up but it makes the car sound more like a noisy diesel. The engine noise is acceptable once warmed up.
Mazda have clearly developed some clever technology to achieve good economy and handling. They now need to devote much more effort to improving overall noise levels and refinement. I have some other negative observations which I'll post at a later date once the car is properly run in. I don't think this car is going to be a long term keeper for me.
What is a "facelift model"? I'm surprised, after reading all the concerns voiced on this thread (there are others as well on this website) that you purchased the car. Caveat emptor I guess. I leased my car, a 2017 GT, about 3 weeks ago underestimating how I would feel about the road noise. I agree w/what you said about It. it's pronounced and envelops the cabin, like an amplifier of road noise. It has a raw feel.
I think that there is something to be said for an observation on another thread that Mazda's making the cabin itself more quiet on the 2017s to filter out wind noise, and creating such as elegant interior, (counterintuitively) magnifies the impact of the road noise. Having a hatchback vs a Mazda 3 sedan also probably contributes. I drove my car back from our airport here in SF about 15 miles to Oakland and the noise on most roads was really loud. It left me feeling numb. I don' have any issue w/engine noise or rain falling on the car roof.
I'm replacing my tires on Tuesday and will report back how much of a difference they make. They are about the quietest tires in this class. It's also obvious that noise is a subjective thing. It's clear that for many, it's not a big deal.
We have to take those at their word who don't feel the Mazda 3 suffers from road noise. Some concede the Mazda 3 does have a lot of road noise, but feel that is offset by its driving characteristics OR that "feeling the road" is not noise, but an integral part of the Mazda driving experience. Re: all of the latter, I'm not one of them. Stay tuned.