Just had new wiper arms fitted but when i put the wiper on it starts with a bit of a clonk? Any ideas as to why or what

The wiper arms can be quite hard to remove if they are jambed hard on the splines. I have no doubt that some people would twist the base of the arm from side to side to remove the wiper arm which can distort the wiper linkage. This may be your problem. I use a special puller to remove wiper arms from the spined shaft which does not impose any bending force on the wiper linkage.

You may need a new wiper mechanism to get rid of the problem.

I just carefully used a standard 3 leg bearing puller, but just used 2 legs. Came off easily. I'm in the shed, I'll be back in the real world in a minute.