Little update; I have noticed on the seat post, if I hold a cloth and run my hands a long the post, there is an obvious but small dip in the middle where the post was at my perfect height and it has a width of about 1/4; it is also only at the back of the post where the bolt secures the clamp. Also when I insert the post there is a lot less resistance where this dip is and requires the clamp to be tighter than other locations on the post.
If I set the hight really high, too high for me, I can not create the clicking noise. The same goes for if I set the seat really low. A few inches either side of the dip and the noise is easy to create by hand.

I'm thinking, if it was a crack in the frame then setting the seat at a high hight would make perfect leverage making it easy to flex the frame disturbing the crack. I have checked the weld points all over the back end of the frame and I can not see any cracks and I have also checked in the seat tube and I can not see anything obvious.

Would 1/4" wrapped area compromise a large segment of a seat post and could this be causing the clicking/creaking? Is it not unheard of for new posts to develop dent/dips ? Weird for a brand new stock seatpost...

Tried to get hold of a different post to swap and test but couldn't today so will try tomorrow.