Hello. My 2nd floor shower has a slow drain, I treat it with Liquid Plumber or Draino. It is not too bad, but when I turn the shower off, there is still some standing water in the tub. As it drains down, I guess there is a back up in the drain pipe, causing the drain pipe to “hiccup” (for lack of a better word) some of the water trying to rush through it. This causes a noise which is real loud on the first floor—could it be the pressure is moving the drain pipe and making it bang into a 2×4 or something? If so, short of going in the wall to secure the pipe, is there anything that can be done, any industrial strength drain cleaners besides what is available at the grocery store? Thanks for any suggestions