I've flashed the latest cm11 nightly and will continue to do so every day. The version I am running now is 11-20140115-NIGHTLY-p880.
After a clean restart outgoing calls work normally. After a couple of outgoing calls in call volume drops dramatically (I can barely hear the ringing tone before the other person picks up and then I can barely hear the other person talk). Incoming calls work normally. The problem continues until I restart my phone or I get an incoming call. Then the same happens all over again, first two - three calls work normally then in call volume drops.
I've tried making calls with and without a Bluetooth device and with and without the stock dialer. I've also tried merging calls and putting calls on hold after I call but the volume problem persists until I restart the phone or I receive an incoming call.
I will continue to update this thread as I flash nightly updates daily.
Thanks for your help