There are two Samsung 2TB HD204UI bought together (their S/N is different just by one digit at the end, so they had to be next to each other on the assembly line), but they behave very differently in tests, as you can see here:
http://forum.hddguru.com/samsung-2tb...ly-t20154.html

Do you think those HDDs should be RMAed?

Could you please test yours HDDs for comparison.

Many thanks.