I live in a newly gut-rehabbed condo building with 6 units total. From time to time, I hear a ticking (only one tick at a time usually at multiple second intervals) in the walls. Sometimes it occurs when we are using in the bathroom and sometimes it occurs when we are not using any bathroom plumbing (or any plumbing in the condo for that matter). What is causing this? Is this a problem that I should talk to the builder about? Thanks for your help!