Tick Over Lumpy

Hi guys baffled over my bike, I've reached the end of my tether and cannot for the life of me think whats wrong.
She runs fine pulls like a train and plugs are perfect

Starts on the button but has the annoying long wait before I can ride her unless I want to ride off on choke at 6k rev's !!!
Once warm she's fine riding away etc.
But with tickover set around 1000 she has this nasty little knock or noise from the bottom end ?
Carbs are spotless and I've done a static balance, it seems to be on number 4 cylinder but I spotted plugs and leads with number 1 and it still remains, engine done about 10,000
Airbox rubbers are all good I've waffed my blow torch around the carbs / head rubbers and there's no increase in rpm.
You might be able to hear the noise on the video....

Stock jets etc but as mentioned she pulls great and plugs are all good ?
Would appreciate any idea's ? I've not messed with the cam chain tensioner or valves.

Static balance is just the starting point. Vacuum balance on a running bike takes in to account each cylinders wear/conditions. 

Would my symptoms suggest just out of sync at low rpm and not noticeable at higher rpm ? Are these bikes prone to lump running when even slightly out of sync ?
I’ll order a set of gauges and see what they show
Thanks for the reply