In the numerous posts about these STB's, no one has ever mentioned this fact. The good news is that it turns off when you turn the unit off, it is also whisper quiet. Does anyone know if the TU-DST50 has a fan. If not maybe this is the reason for the overheating and "green crackles" artifact.
The DST50 also comes with a fan that turns off when the STB is turned off. When using the STB, the internal fan does not do a very good job of keeping the unit cool. I have a high quality fan that I place about a half-inch above the ventilation grille. I found that keeping the fan slightly away from the cover helps lower the noise level.
I once attended a microwave radio maintenance course and the instructor told us that in Europe they would not buy a microwave radio that required a fan because they felt it was a sign of poor design.