Talk about being ANAL.
There's nothing wrong with your touchpad.
The clack you're hearing is the back of the case which is plastic being pushed likely against the Flat battery pack, then flattens out, sticks to the battery or something flat and upon release it returns to it's original position making a tap or a clack sound.
Here's a farkin idea,l STOP pushing on the back of your case with your thumb. Why would you do that?
Some people just take the SLIGHTEST of things and make a big deal out of it and want an RMA. Then they ***** and moan about their RMA being a refurb.
YOUR TOUCHPAD is fine!
If you really want to get technical. The battery is roughly in the center of the touchpad. If you have not noticed, the back of the touchpad is a bevel, it's not flat. A battery pack is FLAT. When you lay a flat object on a beveled surface, there will be a gap in between. So that's where this gap comes in and when you push, it flattens against the battery.
Again, QUIT pushing it in.