The search function would of come in handy here, I must of written this about a million times.....
The problem is due to the microprocessor that runs the whole show, or more precisly a part of it that remembers the volume level you had set when you removed the key, this memory is called EEPROM,(electrically erasable programable read only memory).
It can remember its data without power being applied, however this type of memory had a limited number of write cycles (number of times it can be re-written, around 10,000 times).
The early concert radios would only write to this memory when the radio was switched off, so that equates to 2-3 times a day in normal use, but the later radios have a software bug that writes (updates) this memory EVERY time you alter the volume level, you will quickly use up the 10,000 write cycles and the memory becomes defective, the symptoms are full volume that cannot be controlled, and it will be temperature sensitive often improving when it warms up.
This product was defective from manufacture. EEPROM has limited write cycles any engineer knows this, and the software is defective.
The fix is to replace the microprocessor that has:
1. New EEPROM onboard
2. New software that doesnt wear it out.
The bad news is that this fix is more expensive than the cost of a used radio.
(it's concert chap 
