Could be the blue CRT shorting out. I had the same problem but with red. Eventually it shorted out completely. If it is only 2.5 month old it should still be under warranty and they will fix it.
Do you have the tuner locked out for use of HDMI input only?
Most of the time when a selection is not able to be hi-lited it is
because a feature that is activated locks out other selections.
Hope this helps,
Skyassoc
It sounds like feedback from somewhere else other than your tv like a overhead light or a blinder suggest using a surge suppressor to help block spikes of this sort.
Because this was 3 years ago It would now be cheaper to just replace the unit altogether and you would be alto happier let alone you would have a SMART TV as well.