Thanks for your replies, currently running diagnostics in initial position in the case. The sounds were audible from 5~6 meters (only very slightly).
When I ran the quick test (which it passed), the HDD made noise like it was an engine for a few seconds, after which a repeated clicking noise (different from initial noise) was audible through the case.
What amazes me is that my case is silence oriented (be quiet! Silent Base 800 - Window). At the start of the longer test (currently running, the HDD also made a lot of noise, but it's now quiet and inaudible when my ear is next to it and the case is open.
The drive seems to be working fine (no stuttering, 64 megabytes/second transfer speeds), other than the noise coming from it when installing games.
Will update after longer test and after I have tested different positions inside the case. If the problem persists I will contact the supplier.