We just bought a 30 year old house with PVC drain lines. There is a loud ticking noise in the drain line when running water in the upstairs bathrooms. i think it is worse when running hot water but haven’t really been able to narrow it down that well. At first i thought it was a dripping noise but it is way too loud for dripping.
I think it might be expansion in the pipes but that seems odd since they have been i use for 30 years.
Yes it is the pvc expanding and rubbing againt the wood making the noise, not much to do but tear into wall and correct. What happened is when they knoched studs the made to small of knoch when pipe expands it rubs the wood. let me know.