Everytime I run the washing machine (located on the first level) there is a strange vibrating / humming noise that comes from inside the wall. The noise is not coming from by the machine, but it sounds like its coming from the other side of the house. It only makes that sound two times during the cycle, and lasts about 30 seconds each time. We have now noticed that the sound also occurs when we turn the shower in our master bedroom (located on second level) off. Our home is about 8 years old, and to my knowledge nothing has been replaced since construction. What could be the problem??