I recently purchased a WD Blue WD20EZBX HDD. I already have a 1TB 7200 RPM WD Blue in my PC, and I never heard any annoying noises from it, so I hoped this would be the same. However, the new HDD is sporadically making very strange, pulsing noises even though it is not under load. I tried to record it: https://sndup.net/99st Unfortunatly it did not come out very well, but you should still be able to hear it. Does anyone have a clue what could be causing this annoying noise?
That just sounds like the default electrical hum of an HDD. It doesn't have to be under load to have it be reading files off of itself (like opening dialogues and the File Explorer). Generally, that hum is just it reading/writing small caches and system dialogues that need to be loaded. HDDs work by spinning disks and putting down an arm to tap magnetic 1's and 0's into the machine, as well as read them.
TL;DR: It's the normal hum of reading system files. You could return it or ignore it, but it doesn't strike me as odd.