Diagnosis
The new sanding pad is not seated correctly or is defective. The clicking is the pad hitting the dust shroud.
How to Fix It
Remove the pad. Inspect the plastic alignment nub on the back of the pad. Is it broken or misshapen? Inspect the spindle on the tool for debris. Reinstall the pad, ensuring it drops fully down onto the spindle before tightening the screw. Hand-tighten only; do not overtighten.
If That Didn't Work
You may have a non-OEM or incompatible pad. The DCW210B uses a specific 5-hole hook-and-loop pad. A pad for a different model will not sit flush.
Heads Up
The retaining screw has left-hand threads. Turn clockwise to loosen, counter-clockwise to tighten. Forcing it the wrong way strips it.