I am having problems with the sound of my TV 40PFL9704H/12, connected to a MOTOROLA (NLD KPN) settopbox. Frequently, after turning on the TV, there is no sound. Disconneting and then reconnecting the HDMI cable between TV and settopbox solves the problem, but after switching off, the problem often reoccurs. The settopbox and cable have been changed, but the problem stays. Who can help?