This is another common problem when working on your instrument and you forget to make a note to where your wires are connected. Many times the output wire from the volume control and the ground wire are reversed. This makes all the strings and grounded components noisy and buzz when touched. Many times the wires are connected wrong at the jack when it is replaced. Many times the instrument will read properly using an volt/ohm meter and the noise will not be noticed until the instrument is plugged into an amplifier which can be when you are plugging in at the gig. Check your repairman’s work after having work done to your instrument. It’s a good safety precaution.