Several days ago the Nexus 6 received it's update to Android 7.1.1 which was great news as the device had been sitting on Android 7.0 for quite some time. The only issue is the new update came with a nasty bug which caused a speakerphone echo. This bug caused the person on the other side of your call to hear an echo when you had the phone on speaker. Sometimes the sound would actually be a squealing sound which would make the call unbearable. The good news is that Google has already included a fix for this bug with yesterday's March Security Patch update.
via AndroidPolice