I think it's best to call Miele. There are two sensors in the dryer: 1) one on the three long paddles inside the drum to read fabric moisture and, 2) one inside the exhaust plenum to monitor heat and to shutdown the unit if the exhaust gets too hot, thereby notifying you with the panel light. Either the exhaust sensor is bad, or there is something obstructing the exhaust in the machine itself. Someone earlier mentioned that they found a part, located within their 9800's exhaust, out-of-skew when they checked their unit. However, I would not mess with it, and while the Miele Tech rep is there (insist that a factory Miele tech rep. comes as they have the software, and hardware to properly work on your units) ask them to also upgrade the firmware on both your washer and dryer, if needed.

I need to clarify a bit more...the are two types of sensors in the dryer: 1) moisture and 2) heat. There are two heat sensors that coordinate between one another. If there is not obstruction in the exhaust plenum they can also adjust the Sensitivity setting in the firmware that monitors for obstructions inside the dryer; they can reduce the sensitivity. Also, please read my post here: Self-Destructed

I had the same problem. Could not believe that something else could be wrong with the vent / duct until I climbed onto the roof and checked the outlet. A pad of lint (1/4 inch thick) has accumulated at the mesh which covers the outlet to protect against small animals / birds. Easy fix, just be careful and don't slip... No problems since then and drying times even shorter.
I still have the metal ratteling / banging sound when drum rotates clockwise. No annoying noise in counterclockwise spin.
Let me know if anyone solves that. I am about to get an inspection camera and check out what's going on inside the exhaust while drying.