Hello, I've recently purchased a home. In my kids' bathroom, when either the sink or shower faucet are run, there is a tapping noise behind the toilet (kind of like a finger tapping slowly on the drywall). It doesn't seem to matter if it's cold water or warm, but I did notice a couple of times that the toilet water was gone. Does this imply that a vent on my roof is clogged, causing a vacuum (thus creating the sound and sucking water from the toilet bowl)? Thanks!