Is this loud humming from my refurbished enterprise hard drive normal?

I recently bought a refurbished Seagate ST2000NM0055, and it frequently produces a noticeable humming sound while powered on. At first I assumed it was resonating with my computer case, but the noise continues even when the drive is outside the case. It becomes much quieter when the drive is resting flat on padding. SMART reports no errors. My other drive, an ST2000DM006, does not make the same sound, so I'm unsure whether this is typical for an enterprise-class hard drive or whether I should request a replacement.