I purchased a 40" Sony XBR4. About 20% of the time I turn it on and have no volume. I get the volume back by changing the input from the cable box to my blu-ray and back. I also get the volume back by pulling out the HDMI cable at the TV and putting it back in. I replaced the cable box, same problem. I replaced the HDMI cable, same problem. They replaced the TV, same problem. Any suggestions?