I installed a very nice basement suite in my house and put new plumbing all throughout it. The drain pipe into the basement from upstairs is incredibly noisy – it sounds like a waterfall. The drain is plastic – is there any kind of insullation that can kill the noise?
You can try wrapping it in a pipe insulation such as a poly foam, if this is still to noisy about the only thing that I see that could help is to replace some of the pvc with cast iron pipe.