I have a bathroom on the second floor above my kitchen. The shower, bath tub, and drains for the sinks tie into a 4" PVC drain pipe beneath the toilet and runs down thru the walls in the kitchen into the crawl space below the house. When I run just cold water everything is ok; however, when I run hot water I can hear what appears to be a "dripping" sound between the walls in the kitchen. This has been going for years, there is no appearance of any water leaks or damage anywhere, and I have simply ignore it. We are planning on selling the house and I know the dripping sound is going to be a problem with any potential buyer. I would like to get it resolved, any suggestions. Again it only "drips" when hot water is run upstairs in the bathroom.

Thanks for your advice