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Really is an annoying reminder noise. If anyone knows how to change the sound please let us know.

Holy crap yes...I assume if I try hard enough I can find the actual sound file buried in my user folder and just replace it. Is it the task finished sound? I can't even figure out where it's coming from. But its not pleasant at all. Very odd for Apple.
 
It is possible to change.

Don't think you can change all sounds. They are hidden in deep locations. This works because the Calendar and Reminders both rely the system sound,"Basso" as their default alert sound. That sound is located in /System/Library/Sounds and is called Basso.aiff

Here is what to do (In this order):

1. Delete Basso.aiff
2. Find a better alert sound
3. Change the name of the sound to, "Basso" and convert it to AIFF so it should now be called, "Basso.aiff"
4. Move the file to /System/Library/Sounds
5. Restart the computer
6. Now your default alarm for Calendar and Reminders has a great sound. Enjoy!
 
Don't think you can change all sounds. They are hidden in deep locations. This works because the Calendar and Reminders both rely the system sound,"Basso" as their default alert sound. That sound is located in /System/Library/Sounds and is called Basso.aiff

Here is what to do (In this order):

1. Delete Basso.aiff
2. Find a better alert sound
3. Change the name of the sound to, "Basso" and convert it to AIFF so it should now be called, "Basso.aiff"
4. Move the file to /System/Library/Sounds
5. Restart the computer
6. Now your default alarm for Calendar and Reminders has a great sound. Enjoy!

Hey, why are there no sound files within this file directory on my system 10.8.1?
 
Hidden Files

  1. Open Finder
  2. Open the Utilities folder
  3. Open a terminal window
  4. Copy and paste the following line in:
  5. defaults write com.apple.Finder AppleShowAllFiles YES
  6. Press return
  7. Now hold ‘alt’ on the keyboard and right click on the Finder icon
  8. Click on Relaunch
  9. You will now be able to see any hidden files or folders. When done, perform steps 1-8, however, replace the terminal command in step 5 with:
  10. defaults write com.apple.Finder AppleShowAllFiles NO
 
That's odd, mine is simply blank..? I waited patiently possibly thinking it was loading, but nothing!

There is a sound folder for your user and a sound folder for the system. I was just doing this, and one of them was empty - but the other had the sounds. I hope that's the case for you as well. I had to hold option while in the GO drop-down to find my library. They keep making this harder and harder by trying to make it so easy...
 
Use Secrets from Blacktree

There is a free preference pane called Secrets which gives an interface to a bunch of Terminal tweaks. One of them allows you to change the notification sound in Calendar by changing the name from Basso to another Apple sound. http://secrets.blacktree.com/
 
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