I’m sorry guys for not making it clear. Sorry for the confusion. Let me try to explain it in a better way.
When I flush the toilet it makes a vibrating/knocking noise. The blue plastic part (red circle) drips after flushing for quite some time. Also there is dripping by the (green circle) area. I am assuming I will need to change the whole tank so that it cancels out all the possible faults! I hope this makes much more sense! I think another possible problem is that the toilet wasn’t properly installed by the builder. I did some work in the house and the toilet had to be fitted back. It never use to make that noise originally.
Yes, that is a much better explanation, thank you. It is dripping after
the flush and after
it has refilled the tank, plus of course the noise when it is refilling. You could remove the fill valve, after turning off the water, clean the valve up and fit a new washer (you may need to replace the thin fibre washer, between fill valve and the pipe fitting), but the quick, not very expensive and more certain fix is to replace the entire valve with a new one. It is a common style of valve, easiest way would be to remove it and take it along to a plumbers merchant and ask them for an identical one.