The libaudio.so you replace will correct the ringer problem with the 10/11/11 release of CM7. You can download the file
here.
You'll have to extract the libaudio.so from the libaudio.zip file; it's not flashable. Extract it to some obvious place on your SD card, e.g., /sdcard/download. Be careful, because the next steps require you to change permissions...
1. Basically, open up a terminal emulator. Make sure you have root access by typing "su".
2. type: "chmod a+wrx /sdcard/download/libaudio.so" (no quotes) then hit return.
3. Type: "chmod a+wrx /system/lib/libaudio.so" Hit return.
4. Type "cp /sdcard/download/libaudio.so /system/lib" Hit return.
Should do the trick. Then reboot. This is commonly felt to correct the microphone squealing issue, but I don't think it does. It just fixes the ringer problem AFAIK.