However, there are a few other possibilities, although less likely than a bad bearing:
* Loose debris: Something might have gotten lodged in the blower motor housing, causing the noise. This is less likely to be a constant clunking, though.
* Worn blower motor resistor: While this usually causes inconsistent speed or no blower at all, a failing resistor *could* contribute to unusual noises in extreme cases.
* Worn blower wheel: The blower wheel itself could have become damaged or unbalanced.
Before you replace anything:
* Check the fuse: A blown fuse could be causing the motor to try and start under strain, leading to the noise. (This is a quick and easy first step.)
* Try tapping the blower motor housing gently: Sometimes a small obstruction can be dislodged. (Do this with the blower OFF.)
If the clunking persists: You'll almost certainly need to replace the blower motor. It's relatively inexpensive and often accessible under the dashboard, although the level of difficulty varies by car model. You can find videos online demonstrating replacement for a 2003 Pontiac Grand Prix. It's a job you could potentially tackle yourself if you're mechanically inclined, but a professional mechanic can also do it relatively quickly.
Replacing the blower motor is generally a better approach than trying to repair just the bearing, as the cost and effort often outweigh the benefits.
