Pipes started groaning something fierce once the temps started dropping. Usually they groan after someone takes a shower. I think it is related to the hot water side. The groaning is inconsistent. Happens about half the time and always once the shower is over never during. Any ideas? Thanks in advance.
Best guess : The hot water pipe is secured too tightly to the joists and / or a 90* is wedged against a joist.
The pipe will expand slightly when hot water goes through it - then as it cools - it contracts , causing the noise.
Pipes should hang in their hangers with just a touch of play so they can move.
If you can get to the pipe hangers - try loosening them just a kiss. Also - look to see if the pipe jams against anything that could restrict it's movements.
They say that life's a carousel - spinning fast, you've got to ride it well.
Thanks, I think I found it. It was a bad faucet in the head next to the shower. It had been not working right for a while and when I replaced it, all groaning has stopped.