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.
This is likely caused by one of your fans. If one has collected dirt over time it can cause a loud humming sound when active. Try and figure out which one is causing the noise, if it's not the CPU fan, you can probably clean it yourself using a can of compressed air or a vacuum cleaner (careful with the PC components!). If it is the CPU fan, it may be best to have an expert clean or replace it.