We have issues with the plumbing in our old apartment and we have vibrations in the floor, especially after we have flushed a lot of water like after a shower or running the washing machine. There's also a low frequency humming all over the apartment. I'm thinking there must be some pipes under the floors in old apartments that's causing the vibrations and humming ? The parquet flooring is also really bad in the living room, where it sinks down in certain areas when we walk on it.