Fed up with the racket - can I unplug the fan without doing long term damage? Does it *really* need it? I'm happy to leave the lid off the enclosure if that makes a difference.
Can you not get a replacement fan?
If not then you could buy an external hard drive caddy and move the hard drive into this. The new one may come with a fan in it but they do not always have a fan inside.
Running the old one without the fan should be ok if you leave the lid off it.
Open the enclosure and check the drive - most modern drives will run just fine without a fan.
I had a crap enclosure with a fan. Bought a newer enclosure. No fan, same drive, no problem.