So, I have a Samsung HD103SJ 1TB HDD that I can't even hear the noise, and it's 7200RPM, but when I put the Seagate ST3400620AS 400GB HDDs from the old PowerMac G5, and when it turns on it is very noisy.
Here I use Noctua fans and aircooler precisely because of the reduced noise Max. Acoustical noise 22.6 dB