Rename the default snd file (/system/etc/snd_soc_msm) and replace it with the one contained within the first TAR attached to this post, making sure it has the same ownership and permissions applied as the renamed original, then reboot and test.
Note: If you still experience the annoying whistle during speakerphone calls with the first mod, try the second and finally the third for the more sensitive of devices.
Alternatively, you can flash the ZIP in recovery, which also enables PSM in custom ROMs and replaces the shutter/focus camera sounds with more realistic ones. The ZIP is what I flash after updating CM, hence the name. The ZIP contains the first mod of the snd file, so unpack it and replace that file with the second or third one if necessary to make your own custom flashable ZIP.