The congregation at St Michael's Church in Alnwick, Northumberland, heard the word 'Jerusalem' and references to the resurrection boom out from an unidentified source.
It was only when the Rev Chris Andrews investigated that he discovered his new microphone was transmitting on the same frequency as that of the Rev David Herbert, who was preaching at St James' United Reformed church 300 yards away.
Now they have sorted out their problems to make sure they do not interfere with each other's services again.
Mr Andrews said: 'Every so often we heard a strange voice bellowing out from the unknown. We have had a good laugh about it since and have even talked about relaying services to give one of us a day off.'
Mr Herbert said: 'Chris and I are colleagues and work quite closely, but we never thought we would be working this closely. It certainly gives a new meaning to church unity.'