Hi there - hope you can help

I have owned a Sony Bravia KDL46EX1 for 4 years - without any issues whatsoever. The screen is mounted on a wall about 10 feet from the base unit. The TV is operated through a Sky box (via an HDMI cable)

In the last 6 weeks - we have been noticing intermittent sound problems with the TV. On switching on, the sound is very interrupted (and on off), which will usually rectify itself within 20 minutes. However, this interruption sometimes comes back when viewing TV for a few hours. I tried to watch a football game last week - but the sound was either completely gone or interrupted for the entire game.

The base unit has not been relocated - nor have we put anything near it to cause interference. We dont have any external sound system working off it - and the sound problems persist when using Google Chromecast as well as when watching DVDs i.e. its not the Sky box causing the issue either.

By and large - the picture quality is not affected when we have these sound problems. However, I did notice yesterday that there were white interruption lines rolling down the screen for a time as well.

Is this a known issue with this model? Do we need to make any firmware upgrades on the TV? 

Could the sound card be gone on this TV already after such a short period? We paid in excess of £1,000 for the TV - we would have expected many years of use before having any problems like this

Any help would be very much appreciated