August 30, 2009
Update: details may change in new versions of AE, for example see Change After Effects CS5 render sounds.
You can turn off or customize the sounds made by renders in the Render Que in After Effects. You can replace the render-complete sounds on Windows by adding files named "rnd_okay.wav" and "rnd_fail.wav" to this folder in Windows XP and Vista:
C:\Documents and Settings\[user_name]\Application Data\Adobe\After Effects\9.0.
You can also turn off render chimes by setting "Play sound when render finishes" to "0" in "Adobe After Effects 9.0 Prefs" file (in the same location as above for Windows, or for Mac in Users/[user_name]/Library/Preferences/Adobe/After Effects/).
On Windows Vista (one copy anyway), getting the "Happy-Happy-Joy-Joy" sound (Lynda Weinman's phrase for the original successful render sound) to return after render doesn't seem to work by changing the "Adobe After Effects 9.0 Prefs" file to "Play classic render chime" to "1".
This info is in AE Help, but it doesn't have info on how to replace sounds on the Mac. Information on the web seems based on old methods for Mac OS 7 to 9, but there's likely a way mucking around in Mac folder archive contents or experimenting with a resource fork editor like ResKnife.