I see where you mentioned what appears to be rust. Have you removed the blower motor to see the condition of it inside the HVAC box?
Since it started to move when you banged on it, I have a feeling the motor itself has failed. It's likely that coolant or other liquid has made its way into the motor area causing damage.
We need to pull the motor out and inspect inside the box. Also, if you haven't already, check the cabin air filter to make sure mice didn't get in there and are making a mess. The cabin air filter is located under the hood at the top of the firewall.
See pics below.
Images (Click to make bigger)
Sunday, September 22nd, 2024 AT 8:58 PM