Question External HDD starting up when opening files in other drives.

[PhilboBaggins]

I have an old external HDD plugged in that is very slow. It usually takes a second when I open it for the first time in a while and I can hear it start making noise. The problem is that sometimes I open a file that's not in that HDD, like in my Desktop, and it will sometimes take a second to open and I can hear the external HDD start up. What's up with that?

Windows 10