For long, the problem of safely eject never solved

I have been researching on web and trying different third party tool but none of them actually works.

A lot of time, not always though, I can't safely eject USB portable hard drive. However, I am 100% sure that no files on that drive is running. It's probably the hard drive being occupied by
something in the background that I don't know.

The problem of not safely ejecting is that the hard drive keeps spinning vigorously (I can feel) unless it's safely ejected. Every time if the hard drive can be safely ejected , I can feel by touch that the spinning stops immediately and I can feel safe to unplug the USB cable.

What is the real solution ? Or if there is actually no real solution to this problem?

Yes, annoying problem. Few things you can try. Device may be suspended. Here's how to disable (ignore last part if icon always appears) -
USB Devices Not Staying Connected

For current device eject - Win+R; rundll32 shell32.dll,Control_RunDLL hotplug.dll ,Enter

You can also create a shortcut by r-click on desktop>New>Shortcut.
Put rundll32 shell32.dll,Control_RunDLL hotplug.dll in 'Type the location of the items>Next and name it, like 'Safely eject' and you have a backup method if nothing else works. Good Luck