Ok, I think I will live with the original 7 plus that I got last week, which has the clicking sound.
I bought a 2nd 7 plus hoping the clicking sound will be gone. If the phone is perfect, I would refund the original phone. Surprisingly, the 2nd phone has no clicking sound at all, but it has 3 dead pixles, which is even worse than clicking issue. I checked out the phone the Apple Store and got it refunded on the spot.
On the next day, I gave another try hoping the 3rd one will have no clicking and no dead pixels. Sadly, it is even worse, this one has no clicking but it has 1 dead pixel and a chipped paint on the metal body, which makes the phone looks cheap. Refunded the 3rd one. Live with the 1st one.
Now i am so disappointed with the QC of Apple in these recent years. They build fantastic phones but their QC is worse than any other manufacturers, such as Samsung or HTC.
So for many of those's phones that do not have clicking sounds, i believe they might have other issues that they were not aware of. Dead pixel is the most common and unacceptable issue, it has been around since my first iphone.