Lagging hard disc on Windows 10

Question

I have a quite peculiar problem.

I have my OS (Windows 10) installed on an SSD drive, and in addition I have a "normal" hard disc as data storage.

As of the last three days the storage disc has acted strange. Sometimes video played from this disc stops for up to 30 seconds, Any file from that drive I'm editing and trying to save is unable to save, but when trying some seconds later it usually works, copying files from this drive to my SSD drive sometimes stops up, and then resumes in 5-30 seconds.

So it seems that all operations, both read and write, "hangs" for around 5-30 seconds, and the han happens everywhere from 1 minute to 1 hour between (as noticed when I was watching a movie the first time this occured).

If I copy a movie to my SSD drive the copy itselfs stops up and starts as described above, but when the copy is done, it plays perfectly from the SSD.

I have some files that I have altered many many times the last days. Sometimes when I save it hangs, but I have seen no case of corrupted data anywhere.

So what do you guys think? Can it be a faulty disc even if it's not producing any corrupt data? Can it be something software/OS related?

UPDATE

I also see in Task manager that the load on the disc is reported as 100% even if no applications is reading/writing to it. That can't be good. It seems I better get things backed up here in a hurry!