EXTERNAL NOISE:

External noise can enter the experiment via unwanted AC signals coming from nearby instruments, motors, or other experiments, and capacitively coupling into the experiment via stray wire or other capacitance. The most common cause of capacitive coupling noise results from stacking instruments too closely together, which results in frequency pick-up from neighboring instruments. For example if there is another lock-in amplifier near yours that is being used for an experiment in the neighboring magnet, the lock-in oscillator signal could enter your experiment via one of the signal carrying wires, which have some small capacitance. To minimize this noise, turn off or move all instruments not in use, and use wires with minimal capacitance.