I just got an older second hand Kenmore washing machine about a month ago. It was working like a charm up until a couple of days ago. The washer seems to drain all of the water at the very end of the whole washing cycle but then in about 5 or 10 seconds I can hear the water rushing back through the drain tube and back into the washer. This leaves the clothes sitting in a pool of water. Any ideas on what could be wrong with either the plumbing or the washer? Thanks in advance.