On the highway or irregular pavement, the Acura RDX produces more cabin noise than expected for a vehicle wearing a luxury nameplate. And while some on staff gripe about the sound of the turbocharger, that's not a problem for me. What I can't get past is the note of the four-cylinder engine, which only reminds the driver that a more sophisticated and smooth V6 engine isn't pumping away on the other side of the firewall.