Maybe a sign I've given it covid? The cistern - side lever, not top button - or even the supply & drain pipes behind it has started making a sneezing type of noise which I notice when the cistern is full, about once every minute or two minutes. Might also happen when the cistern is empty but it's not empty for long so can't be sure. I've had a look online to see if I can find what the problem is and can't see that as a common thing anywhere. The cistern seems to be working OK other than that - flushes OK, stops when full, no mystery flushes. The clear plastic tube which hangs down into the water (I'm sorry I don't know the correct name) is split but I suspect that wouldn't be in use once it's full. Can anybody guide me on what this problem might be? I'm grateful for any advice!