Eco engine noise mode is how I run my GTD... its pretty much off. Mind you in "normal" I didn't think it was making much noise (compared to sport), but switching it down to Eco definitely dropped a lot of what I perceived as road noise from Normal... it does just come across as road noise at Normal levels too. Sport has a snarl (ok, artificial and fun sometimes but not for long journeys!)
I don't reckon you'll notice it at all.
If you wanted to completely kill it to zero, OBD11 is probably cheaper to buy then get the dealer to do it for you.