Quieter than a motorcycle?
You can certainly quiet down a barebones car if you want to. More than a couple of Mirage owners have stripped out the interiors and plastered on that sound deadening stuff ... those big squares of peel-and-stick asphalt/tar.
Ask me again in the spring when I get my 1998 Firefly on the road. I'll be better able to compare it to the the Mirage.
But I suspect they're about the same.