Is that 99% disk space or disk activity? because that's weird if it's space.... I'm thinking you mean keeping the hard drive busy. It could be doing downloads or updates.
See if ur windows is indexing everything on ur pc that will cause the issue i am at work so cannot explain exactly how but google disabling windows i dex options
I have my own line in that, Steam and games have self HDD 1TB WD, OS another, PageFile another, and record or edit another HDD. Now time to go up and search for some SSD M.2