I had a very noisy fan for a long time. Sometimes I could tap it and get it to quiet down. The "genius" bar folks said it was probably a foreign object that had been sucked into the fan.
I finally replaced it and it is a joy to not hear it.
From my experience, the answer to your question is "No, you don't need to replace it." On the other hand, if you do replace it, you may greatly enjoy the beautiful silence that will result. It is a VERY easy repair.
--Kenoli