I think that the current generation Mazda3 has gotten a bit quieter since its 2014 introduction but, still a bit too much road noise according to those who test them. That's too bad as they're a great driving car. The next gen is supposed to fix this. But, Mazda took away the rear independent suspension. Give a little, take a little away!
My advice to the OP is to take the car out on the highway and not just around town for a test drive. It's the short test drive that my suck you in and then(as I've read in many customer reviews), the hiwy noise is cause for concern after you have taken delivery.
I like the Mazda3 very much. We even had an '06 and the biggest complaint is its road noise. But this one didn't ride too bad!
This newest gen IMO, has an overall somewhat harsh ride over broken pavement, depending on trim level for(key word), "EVERYDAYNESS"! Especially as the car ages & for the long haul. Not bad in the South or South West U.S. but, in the Northern states & Canada(salt belt), broken pavement, can you live with this day in, day out, year after year(til the car is paid off)?
In this generation, look for the models coming out of Japan. They seem to be just that little bit better made IMO as I've driven them from Mexico as well. To me, there is a difference and when I drove them back-to-back, I didn't know where they came from until my wife did the CarFAX thingie and it show their assembly country.
I was remarking over how much nicer built this one particular Mazda3 felt that we were testing as compared to the other that we had driven. It was MFG'd in Japan as the other was from Mexico. And again, I didn't have this information prior!