PVC drain pipe that the washer empties into is echoing all plumbing sounds
If you didn't, you should have installed a trap in that drain line to keep noise and smells from coming up the line. Make sure it is low enough to have a good amount of drain pipe above the trap so when the washer drains the water does not overflow from the pipe. If the drain will be inside the wall make sure you use a glued trap so no joint will come loose at a later time.