Garth is complaining that his upstairs toilet has started making a lot of water noise as the flush flows down through the walls. What do to?
If the noise was there from day one, about the only thing you can do is to open the wall and wrap the pipe in sound blanket insulation to muffle the sound. But if it didn't used to make such noise and has just started, obviously something has changed.
When water flows down the waste pipe, it is supposed to spiral round the outside, hugging the pipe and avoiding making noise. If you look closely at the photo from my computer, you will see that it is possible for some sediment or partial clog to be hanging over the open pipe from the toilet run. This can cause the water to go out to the centre of the pipe and fall, making a splashing noise when it finally hits the bottom, or even the side on the way down. This can usually be remedied simply my snaking from the toilet over and down the vertical stack. Take the toilet off to work from the floor, and move the snake back and fourth a lot once it has bent into the vertical stack. That should scrape anything off that lip and let the water flow down the outside of the pipe as it is supposed to.