When I flush my toilet there is a terrible loud noise while the cistern fills. Any ideas ?

When I flush my toilet there is a terrible loud noise while the cistern fills. Any ideas ?
Describe the noise. Is it a squeal? A bang? What? Regards, Tom

It's like a very, very loud hum almost like a ships horn !

Ahh! That would place the falt in the ball cock.The noise you hear is the washer viberating against the seat as the tank fills. The solution would be to shut the water off at the stop and remove the three screws on top and pull the float ball and stem and washer assembly up and out. Pry the washer out and turn it over. Now, with the ballcock still open, turn the water back on to flush the supply out. Now check there linkage between the flapper and the flush lever. It should have 1/4" of play when your tank is filled. Next feel the flat side of your flapper. Does it have wavey edges? Do your hands come away black? Replace it if it does. And last check the seat itself. Any nicks or rough spots? If so click on back. There are replacement seats that glue right over the old one and are easy to replace. One of the above should take care of your howling. This happened in a new house some years ago. Only at night and in the early morning. They thought the house was haunted and were about to move out. I caught it in the powder room toilet. It would vibrate and the pipes in the wall would pick it up and carry it all over the house. Hope this helps, Tom

Thanks speedball1 I'll try them and get back to you, again thanks how do I rate your answer ?

Thanks speedball turned washer over... perfect, cistern even fills quicker now. I'm an electrician and I've asked lots of plumbers on site in liverpool and around the U.K. to no avail then a retired Yank sorts it first go!! Plumbing world lost a star when you retired mate. Thanks again

Thanks for those kind words. I was in your city back in the late 40's. Had a great time there. Cheers, Tom