I have a 1991 Itasca Sunflyer motorhome on a Chevy chasis. The wiper controles, dimmer switch, and cruise control are all on the same lever on the left side of the steering column. When I start the engine, the wipers come on even though all switches are in the off position. After a few minutes I hear a buzzing sound somewhere in the dash and the wipers stop in the normal off position. The buzzing will sometimes stop immediately when the blades stop and sometimes it will continue long after the blades stop. Can anyone help me with this problem?