Why does my MacBook fan sound loud and cause vibrating?

I have a 2.4 GHz (A1278) MacBook Unibody 13" with a really loud fan. Sounds like something is scraping and it vibrates. It's really loud even when I'm not doing anything on the laptop. Everything works fine except my fan noise/vibration.

Note: I opened it up, and cleaned out all the dust and it looks perfectly fine. Nothing is caught and I cleaned out the dust

Please help me with these questions.

Do I need to replace my fan?

Is it safe to use when it's so loud and vibrating?

How do I fix it? Any troubleshooting suggestions?

Thank you!