If I remember correctly on Mac the Finder could cause that – because it accesses a file’s preview in certain display modes.
I'm on a PC though.
...I don't even have any other programs running...
It is impossible to only be running Photoshop. You have a gazillion other processes running transparently in the background. Open task manager to see. It could be antivirus running, a backup process, image preview generation, or some other file system operation that could be related to your new server.
I meant design programs or image previews but thanks for your answer. I will look into it.