The speakers won't affect LCD screens.
But that is a good test, put the set on "zoom", if the red line disapears then
good news, its not your panel.
If the red line doesnt disapear, then look out.
A red line that disapears during zoom indicates a video proc problem,
or maybe a tuner issue, might even be fixable through the service menu.
If it doesnt disapear during zoom then its probably panel trouble,
might want to check for warranties, hidden or otherwise.