I cant hear or others cant hear me properly on a call

Since about a month, I cant hear or others cant hear me properly on a call. The voice comes and goes.
I searched online and disabled Google play services CheckIn service and the phone started working fine for about a week.
Now the problem is back again and I am not sure what to do. Any help please?
I am on CM 12.1 nightlights, Nj2 bootloader and modem, on Samsung Galaxy S3 ATT.