This type of problem is very hard to troubleshoot. I had a hatichi LCD that was doing the same thing. I got a service manual and started tracing the circuit. I thought the lamp power supply had problems. My problem was the switch on the access door for the lamp was loosing its ground. The ground was supplied by the lamp power supply and I had to fix the power supply. There are too many processes that are involved to guess. Of course, I have electronic repair training and experience. The problem will probably get worse over time and if the problem is repeatable such as after off for xx hours it will reoccur a repair shop has a chance. They would have to keep the set long enough to repeat testing and determine if it is repaired. Intermittant problems are not fixed until the set works for days, weeks or months. As a techincian you never know if an intermittant problem is fixed. Only time will tell. I feel your pain but no easy solution.
