I put a brand new HDD into an external HDD enclosure. After copying a huge amount of data onto this drive, the disk head is still processing something even two hours later (the copying process has already finished, but it sounds like the drive is "putting things in place").

Is that a normal behavior?

It does not sound like a defect or anything else, it sounds more like I would still copy things on it and therefore the head moves around. When unmounting the drive those sounds will stop and the drive will still spin, but stop moving the head.

Maybe the OS is adjusting something?