Hi, I have a question about my bottom level bathroom sink (three story town house). When no water is running (or even when it is running) there is a sucking sound coming out of the drain. It is loud enough that you can hear it in the hallway when walking by or near the bathroom.

Can you tell me what this could be? If it is Normal? And if not, How to fix it?

Also, I have noticed a lot of condensation under the sink by the actual plumbing, could this be part of the problem/issue?

THank you for all your anticipated help,