Ok, I've got a colecovision in very nice shape that I'm getting ready to ebay. I tested it, and it works fine, but the sound seemed very erratic. For example with Donkey Kong, I had to turn the volume up to hear the opening tune and the bgm on the first level, but when mario dies, the 'death march' is extremely loud. Other games follow this or a similar pattern. The worst was Pepper II (I love this game) which had a ton of static all over the place.
It seems to be in some way related to the picture, because certain scenes with lots of stuff going on or lots of color seem to generate more static or sound issues than sparse images.