You can do as suggested above with an elevated TextEdit session. Then, copy and paste the original contents of the .plist file into a new file, save as a backup. Paste the following into the original, now empty file, and save it. You may have to reboot.
The contents come from a working Snow Leopard mini, but fixed the issue on my 2010 MBP i7. The mini is an '07 Core2Duo that I own.
Here is the contents of the file:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>EnableTransactions</key>
<true/>
<key>Label</key>
<string>com.apple.audio.coreaudiod</string>
<key>ProgramArguments</key>
<array>
<string>/usr/sbin/coreaudiod</string>
</array>
<key>KeepAlive</key>
<false/>
<key>MachServices</key>
<dict>
<key>com.apple.audio.coreaudiod</key>
<dict>
<key>ResetAtClose</key>
<true/>
</dict>
</dict>
<key>UserName</key>
<string>_coreaudiod</string>
<key>GroupName</key>
<string>_coreaudiod</string>
</dict>
</plist>
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0"><dict> <key>EnableTransactions</key> <true/> <key>Label</key> <string>com. apple.audio.coreaudiod</string> <key>ProgramArguments</key> <array> <string>/usr/sbin/coreaudiod</string> </array> <key>KeepAlive</key> <false/> <key>MachServices</key> <dict> <key>com.apple.audio.coreaudiod</key> <dict> <key>ResetAtClose</key> <true/> </dict> </dict> <key>UserName</key> <string>_coreaudiod</string> <key>GroupName</key> <string>_coreaudiod</string></dict></plist>
Good luck all, this issue had my brain broken.