Hey and I've been through something similar with my blender a while back. That grinding noise started out of nowhere, and it turned out the blades were just a bit loose. Try tightening everything up when you reassemble it. Sometimes that alone does the trick.
If that doesn't help, maybe check the bottom where it connects to the motor. Could be some wear there causing the issue. I ended up lubricating the parts lightly with some food-grade oil, and it smoothed right out. Works great now. Don't stress too much; these things are usually fixable without much hassle.
Oh, and if it's still noisy after that, might be time to look into the motor, but hopefully not.
