Bathroom drain pipe bangs

Since the roof was replaced it seems the old iron drain pipe in the second floor bath bangs once in the morning. I tried snaking the pipe, which seems to help about a day or two. Is this a clog or is it something worse. I don't like the idea of movement. What are you thoughts, experience?
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New & Improved - N/F John wrote:

I am guessing it is an expansion issue as it warms up in the morning. Since you have related it to a new roof, my guess is it is a clamp or some sort of hanger issue at the roof or in the attic area. I doubt if it is anything inside the pipe.
Once you find the problem, adding some sort of shim or tightening or loosening a clamp will likely take care of it.
--
Joseph E. Meehan

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The new roof may also be touching the stack pipe or its the flashing , when sun hits the roof it expands.
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I did a lot of sealing with the house work. I know I spray foamed the pipe in the attic. Other than that and the new flashing I can't think of anything else. I guess I can remove the hard foam and use that softer foam that doesn't expand that much. Thanks Joe and m for your ideas.

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