One Connect Box has a mechanical device inside (assume this is a fan or hard-disc) that starts to make a rotational noise when the power is first turned-on. However, noise will normally cease after recycling power or thumping the top of the One Connect Box. And once the noise stops, it normally doesn't return until the next time I turn the unit back on.
Several videos on You-Tube provide fairly easy process to disassemble the one-connect box so small cooling fan can be cleaned and lubricated. Took only about 15 minutes to complete and this solved the problem.
As a follow-up, the TV (Model: UN78HU9000F - from 2014) displayed an error message several days after I first detected the fan noise, indicating there was cooling fan issue. And this was probably triggered by an over-temp condition since the fan was not spinning effectively. But error message ceased after cooling fan was cleaned and lubricated.
