How DMR-ES15 mechanism sounds?

During recording on “DVD-RW” and “DVD+RW” discs “DMR-ES15” recorder produces constantly very silent (audible when ear is near by case), intermittent sound - something like a “rrr…rrr…” . Is it normal? LiteOn recorder in my computer (and NEC too) sounds completely different (it produces continuous sound). Is it a result of other recording method?