So sorry for the delay James, I was not notified of your reply!
Is the machine on a level surface?
Can you see any obstructions?
What condition is the walking belt in? If the belt is tight, try loosening it. If it is worn underneath, try applying belt lubricant.
Let me know what you find.
The incline unit would not stop the belt from working unless it is causing tightness somewhere - check the tension of the belt and adjust if necessary.
Can you work out where the grinding noise is coming from? Is it from a motor?
Could you upload a short video showing what exactly is happening?