Noisey w.c.cistern

Hi all
Our downstairs w.c. is extremely noisey when flushed.Sounds like a wailing banshee and if used early in the morning/late at night wakes the whole house!This is not the usual noise of water refilling the cistern but happens when the ball cock in the cistern is pressed and held down. Any ideas please? Is it a job for the diyer or do I need a plumber to replace the ball cock and plunger to get rid of this wailing as we have visitors coming soon and don't want to frighten the life out of them!
Thanks
Kenbo

two things you can try, inside the ball cock mech is a cone shaped piece of plastic which regulates the amount , speed of flow into the cistern, they come in various sizes and are easily replaced, once you turn off the water first. sometimes there is a build up in hard water areas and it be cleaned off and re-inserted. any hardware will have a replacement. secondly you can get, make up a small plastic hose/tube to go from where the water enters down to the bottom of the cisten ie the water has no fall as such. a small elastic band will keep it in place

Sounds like a case of water hammer. Do as above and maybe change ballcock if it doesn't work for a high pressure type.