background processes? Network activity mnitoring systems triggering something?
I would suspect that some process running in background is accessing the disk.
Depending on the OS (which you didn’t mention), you may run a tool to see a list of the running processes. On Windows that would be the task manager, and on Linux one option could be the top tool.
I would suspect that my system is running normally.
I think nearly all PCs I’ve worked on in at least the past decade have had system processes that periodically accessed disk. Windows networking is definitely a common example. Various TCP/IP-related processes can also cause access, e.g., a software firewall app might check its database or log an incoming packet.
Screensavers, schedulers, lots of things might wake up at intervals.