Hello and seasons greetings! I was wondering if anyone had any ideas on the following situation: I have had a Kenmore high efficiency front loading washing machine for the past 6 years or so. The first year everything worked fine. Since then I have been dealing with a situation where the drain overflows when the machine is entering the spin cycle. It has gotten gradually worse over time. The drain pipe is 2 inches in diameter and about 3 feet high than the point where it leaves the machine. I have snaked it frequently and sometimes it works for a few weeks or maybe at most 2 months before it overflows again. I have had three plumbers here who also have snaked my drain. They tell me everything is fine and the drain is properly vented yet the problem persists. No other drains are slow. I have also tried adding a nipple to restrict the flow, again to no avail......any ideas....any help at all would be of considerable assistance..thank you

V/R
Ken