@ronsec hit it on the head. The clicking is caused by the IR lens being engaged and disengaged. This is caused by the batteries not being able to generate enough charge to illuminate the LED or IR.
When the camera is in standby, the batteries produce sufficient charge to run, hence why the battery indicator reads fine. Once they’re put under load, they cannot handle it.
A simple battery swap should solve your problem. If it’s in a high traffic area, I highly recommend looking into AC power. They sell increasingly long micro USB cables. I have one running about 30ft under a gutter to a camera. Works like a champ.