Social skills training is a type of psychotherapy that works to help people improve their social skills so they can become socially competent. SST is predominantly a behavioural therapy but cognitive therapy can also be used in some situations to maximise the success of SST.
Often a faulty toilet ballcock (fill valve) will cause resonance sounds like these. At least it's easy to check -- here's how to tell if this is the cause. Close the supply valves to all the toilets. If the noise disappears, open them one-by-one till the noise starts again. Replace the ballcock in that toilet.
At this point it may join the main stack. It is, therefore, possible for a house to have several bathrooms, and only one vent stack going up through the roof. Typically improper venting results in a siphoning or gurgling noise when water is drained out of a sink or tub. A sewer odor at a fixture can.