I found this fix via reddit and it SEEMS to have worked
I think there’s an issue with game logs since patch and it affects slower storage drives.
This has worked for me:
Go to your installation location and then: "retail"
Open the “Logs” folder.
Find the Hotfix file and right click > Properties
Go to Security >Select Everyone>Edit>check Deny for everything
Hit apply.
It’s writing a lot of lines (seemingly errors) in the short time of 1 second after turning in or completing a quest/world quest, looting rares/chests etc. Removing its ability to write seems to fix the problems for me at least.
credit to Avanyaa
EDIT: Some people have reported experiencing launching the game from the Battlenet client reverts the permission changes. Try launch the game from the _retail _folder instead if this solution didn’t work the first time. Make sure the game doesn’t run as administrator.
Blizz replied below; they suggest not doing this. Many are desperate for a fix, they are working hard on it.