The rear speakers in my 2 year old estate with standard radio (not Canton) have always sounded muffled compared with the ones in the front, which have a lot more treble. Is this normal, or something I should be asking the dealer about?

I have the canton system but can relate to your problem. now i usually drive alone so it aint an issue but i tryed to sit in the back and the sound is a lot different in the rear speakers. if i set the sound option to just the rear speakers the sound is terrible compared to just the front speakers.

i use the "front" option in the sound menu when i drive and find that option to work for me.