Feint Lines on Screen

Hi all

I've been lurking around this forum for a while now and have decided to join :)

I have a SKY+ HD box
I was watching the footie on SKY the other day (night game) and noticed some horizontal lines going down the left hand side of the screen.
When I switched channels it was more noticable on the blue background screen
I re-booted my box and still the same, I changed the HDMI lead moved wires etc, but still the same , I updated the software on my TV too.
I switched over to my freeview channels and the lines seemed to have dissapeared so I know its not the TV.
This is more noticable in the evening
The signal strength is pretty good when checking on the box

Any help / advice :confused:

Thanks