rear cassette seems really noisey and clunky.

I have had my Flux S for a while now but have only used it a handful of times but i cant help find my rear cassette seems noisey and a bit clunky.  I have spent time to adjust the rear derailleur but it still doesn't seem as smooth as i thought it would be.  

My bike is a Boardman MTX8.6

I checked the cassette online and i have ordered the right one. I have setup the bike with the correct quick release adapter that was included 

Can you give me some suggestions of what to try next?

I have a video if that helps?