Diagnosis
You've likely got a worn-out or damaged blade assembly bearing, or something very hard (like ice or a fruit pit) has jammed in the blades.
How to Fix It
Stop the blender immediately and unplug it. 1) Carefully pour out the contents and inspect the blades. Remove any obvious hard foreign objects. 2) If nothing is visible, try manually spinning the blade assembly from underneath the pitcher (be careful of sharp edges). If it spins freely and quietly, the issue might be elsewhere. 3) If the blade shaft feels gritty, loose, or makes a scraping sound when spun, the blade assembly unit itself needs replacement.
If That Didn't Work
The noise could also be coming from the motor base drive socket. With the pitcher removed, turn on the blender briefly. If you still hear a grinding noise from the base, the internal motor coupling or gears are damaged, which requires professional service.
Heads Up
Using the Pulse function for crushing ice is okay, but don't run it continuously for more than a minute. Letting whole ice cubes or large frozen fruit chunks jam the blades is a common cause of this damage. Pre-crush very hard items.