The cold water pipe feeding the loo cistern has started a loud and harmonious vibrating noise every time its flushed, any ideas on how I can stop this please??
What type of valve is on the cistern ? it can sometimes be the ball valve that causes the problem, also worth considereing clipping any un-clipped pipework.
Almost certainly the inlet valve. If its a ball valve just replace it - there only a fiver and much quicker than messing about trying to replace washers, cones etc.