Why is my external HDD active when I'm not using it? I have a partitioned external HDD (orange LaCie), with one partition for Time Machine. All partitions are Mac OS Extended (Journaled, Encrypted). The HDD is GUID Partition Map.

I'm not (consciously) doing anything with the disk right now, and Time Machine is turned off at the moment.

Why is the light on the HDD blinking (and the HDD active, because I can feel that)? What is it doing?

I am running macOS Mojave 10.14.5.
It's probably the 'Spotlight' indexing that is busy indexing the drive 's content.