Diagnosis
That's thermal expansion. The ceramic plates and metal housing expand at different rates when they heat, causing pops and clicks. It's normal, but excessive noise can indicate a loose internal component.
How to Fix It
Usually, just let it run through a full heating cycle. The noises often lessen after 10-15 minutes as temperatures stabilize. Ensure the heater is on a flat, level, hard surface—carpet can insulate the bottom and cause uneven heating, making noises worse.
If That Didn't Work
If the clicking is rhythmic or sounds like electrical arcing (a sharp *snap*), unplug it immediately. That could be a loose electrical connection arcing, which is a serious hazard.
Heads Up
Don't confuse normal expansion noise with the sound of something physically rattling inside. If you hear a loose part bouncing around, stop using it—something has broken free.