we replaced the old ballcock with a fill valve in our upstairs and downstairs loo about 18 months ago and about a month ago the upstairs bog started making a horrendous noise when flushed < screechy wailing sound>, followed swiftly by the downstairs one.
I contacted the makers Fluidmaster and they sent me replacement diaphragms to fit to see if that helped. It didn't so let them know; yesterday I received a parcel and it contained two new Fluidmaster fill valves! I have now bored my dh to death as I keep yakking about them 
I was chuffed to bits at the level of courtesy and customer service shown - doesn't happen very often
10/10 to Michelle at Fluidmaster