During post-test data review, a Test Conductor observes a persistent 60 Hz sinusoidal noise superimposed on the signal from a strain gauge. Which of the following is the most likely cause of this data quality issue?

1. The sampling rate of the data acquisition system was set too low.
2. The strain gauge's calibration certificate has recently expired.
3. A ground loop or improper electrical shielding in the measurement setup.
4. The data logging software is incompatible with the sensor type.