Ditto to what Cortez says. I have two bikes (owned lots of others), one with a screen (The DT, both Bondi, and stock screens) and one without, and a few others. And 5 different helmets. If you're pretty well protected behind the windscreen it's quiet. If you have a crappy windscreen, it's worse than a nice clean airstream without a screen, regardless of helmet.
Get the hemet you like. Sound will becomes more of an issue if you do long trips (or are sensitive to sound which it sounds like you are not), and then I'd agree with the above post, get hearing protection. I have an expensive helmet (Full faced) that was rated good on sound protection, and a cheeper (3/4) one that shouldn't be good, but is quieter.
I have a modular helmet too, weight gets to be more of an issue than sound for me with that, don't use it very much because of it. Most modular helmets are not rated to ride flipped up. Meaning, it really only buys the ability open up the chin when your stopped. Been a year since I looked, there may be more now, but something to be aware of.