It is almost like air in the system (Shakes the house)! Does this mean it needs a new ballcock? It was replaced by a plumber about 2 years ago for same reason.. It is a plastic system of ballcock in a reasonably new loo (8years). All the loos in the house were put in at the same time but this is the only one that makes this dreadful noise.
Please advise if you can
Kipper

Sounds like a loose washer in the stop valve to me.

Open this https://www.askmehelpdesk.com/attachments/plumbing/20379d1243960447-leaks-toilet-handle-when-fills-both-ballcocks.jpg which one do you have, I'm betting the one on the left, correct?