That depends on how you've connected them. If you've connected them to the built in fan controller then the fans operate at their maximum RPM to ensure that they rotate without an issue. When you feed the with bare minimum, chances are that they won't rotate to begin with. I'd say you're fine as is but if your're OCD about the noise at bootup then you can grab a fan controller that allows you to dial in your voltage/corresponding RPM for your fans.
I own a Lamptron FC 5 v2 but they also cost a pretty penny thus my point about you being good as is.