why does my toilet make a noise when flushing?

My toilet always makes a loud noise when i flush it. It lasts while the toilet cistern is filling up again. This noise gets much louder when the tap is turned on and lasts untill the cistern is full. This problem occurs almost every time the toilet is flushed, i would say 90% of the time. Is this a simple problem to fix? or will i need a plumber?

Thanks

Andy