Our plumber just installed PVC drain pipe from a second floor bathroom across the first floor ceiling and through the first floor walls to the basement. Whenever we flush the toilet or use the sink, a large amount of very annoying noise can be heard within the first floor area (the noise can be heard in several other first floor rooms surrounding the pipes). Drywall has already been installed in the areas containing the pipes. What can we do to correct this problem? Would installing batt insulation around the pipes work? What about injecting foam insulation into the cavities surrounding the pipes? Please help! We cannout continue to live with this noise.