Hi JasonBradford23,
Thank you for reaching Microsoft Community.
For the volume down key on the keyboard, do you mean the F5 key? Let's isolate first if the issue is caused by the key or the volume rocker itself.
How about the Fn key, is the key lit up? If yes, the F5 key is not suppose to do the volume down function. Can you toggle the FN key on and off? If the F5 key is stuck or being pressed, the Fn key won't be toggled on and off. So if the Fn key can be toggled on and off, the issue might not be on the F5/Volume down key but on the Volume down rocker itself (next to Power button). Please try to detach the screen/clipboard of the device then check if the volume of device stays down. While the screen is detached, select the Speaker icon on the Taskbar, try to move the volume slider then observe if it goes down by itself. If it does, we could say that the issue is the Volume rocker itself.
If the Fn key can't be toggle on and off and the volume does not goes down when screen is detached, we could conclude that the issue is on the F5 key itself. Considering that other keys on the keyboard works fine, this could be a hardware issue already. Please contact support through this page: Contact Us or through our Global Customer Service phone numbers for further assistance and to check for replacement options available.