There's something clogging up my Startup Disk space, I can't find it even using Disk Inventory X For some reason there's something clogging up my Startup Disk space. I can't find it even using Disk Inventory X.
Do you know how to use Terminal ? 
You could install this:
https://github.com/wvangeit/duk
by executing 'pip install duk' using the Terminal.
Then execute 'sudo duk /', and it will show you the space usage on your disk.