Humming hard drive

I just purchased a 4TB 7200 RPM Hitachi internal hard drive for my early 2009 Mac Pro. No problems formatting under OS 10.9.1. My concern is that it makes a slight humming noise, sort of like what you hear from fluorescent lights. None of my other internal drives make this noise. Should I be concerned? (I contacted OWC where I bought it and they have offered to replace it, but if this is normal behavior I don't see the point in doing this.) Thanks.

Steve