I have an 81 year old house with a cast iron stack. About 6 weeks ago, I started hearing what sounds like a slow drip whenever the shower or toilet are used in an upstairs bathroom. From listening to the noise, it sounds like it is coming from an enclosed part of the wall containing the stack. I have opened a couple of holes in the wall, and have also pulled up some floorboards underneath a linen closet to see if I could find a leak, but have not seen any indication of any wetness. I have also not noticed any water spots on the ceiling underneath the bathroom. My question is, is it possible that the noise I am hearing is some kind of expansion within the cast iron pipe and if so, is it a potential problem?

Thanks for any advice anybody could give me as I am at a total loss at this point.

A house that old with cast Iron Stack its very possible that the stack is heavily rusted inside.
If the drip is on the vertical it may not show up easily. To test stack thickness lightly tap with hammer and see if it sounds thin/soft/low thud. They rust from the inside out.

Expansion and contraction will not sound like a slow drip. I never heard a cast pipe make noise except for a drip or wind over the top vent of the stack

I would concentrate on the stack and any 90s etc where a drip could start.

You could get a plumber out that has a camera to go down the vent stack and check the inside walls of the pipe, you might see the problem. When cast gets so old it actually can weep out of its thin wall.

If the pipe is that old I would think the cast here could be in trouble.

Signed 21 Boat

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