OS takes a while to boot, access other drive

Recently installed Windows on a SSD, very satisfied with its performance so far.

However, sometimes, Windows will take an unusually long time to boot, it will just sit there, and then I will hear my mechanical hard drive (data drive, no OS files installed on it, connected via a different SATA port) spin up, and at that point the Log in screen will appear.

I'm curious as to why it needs to access the data drive at all, there is no System Reserved partition on it, and no Windows files as far as I can see. I have attempted to keep it as a purely data storage drive.

Anyone have any ideas on why this is happening?