I have a simple electric motor setup that spins using a simple copper coil rotating around between two metal nuts. The nuts are connected to a DC supply box (on the right) like this:

Sometimes, especially at higher voltages (around 3.0V), the voltage from the box changes on its own (by an amount of ± 0.1V) , and at even higher voltages (maybe around 4.0 or 5.0V, it changes by ± 0.3-0.5V). The box also makes clicking noises like a switch is being turned on and off at higher voltages (something shorting? or maybe a safety circuit? I don't have a manual for this box)

I want to know why:

1. The voltage changes on its own
2. The origin of the clicking sound from the DC supply box