Can anyone offer some advice please? I recently replaced the ball valve arm in my cold water tank in loft as previous one had rusted up and got stuck. I used a high pressure valve - Since replacing it, every time we flush toilet, there is a whooshing sound in vertical pipes to the loft when tank is refilling - Whilst there used to be a sound previously it was fairly quite and unless you were near loft hatch or pipe, didn't notice it. Now it's very loud and can be heard throughout house - particularly annoying at night when children asleep. Lasts about 5 mins whilst tank refilling then quietens down to silent again. I have tried lowering pressure on stop cock (as recently had new sink fitted in kitchen and when installing, the chaps moved stop cock and set it quite high) - but this makes no difference. Any advise would be most welcome. Many thanks.