I have this same issue. Anybody found out for sure if it was just a software bug?

Same problem in a 2009 C300 here. No matter how quiet the radio was when you turn the car off, it starts quite loudly next time you start the car. Very frustrating.

I agree with Jerry that the radio in this car is very substandard in terms of options to control. Compared to VW, Audi and BMWs that I've had, the HK system is very basic. Treble, bass, fader, balance, Logic 7 on or off, and that's about it.

Bringing this back from the dead did anyone ever find a fix for this ?

interested to know if there is a fix. My wife’s 2008 C300 sport does the same thing. You can turn the volume all the way down before you shut off the car but when you start it up again the radio comes on very loud. Annoyingly loud to the point where you have to turn it down. Went to the dealership early on in ownership and they said there are no settings to change the volume when they hook up the computer to it. Wifey has been dealing with this problem for 12 years. Still annoying now as it was on day 1. Anyone find a fix yet?

Nothing that I've found very annoying and i feel like it's getting worse mine adjust constantly up and down as i am driving ive had the system updated at the dealer changed the physical knob on the front of the unit and searched thru all of the settings in the hidden menu without any luck.