I mentioned this on another thread but I thought I'd raise it here. You know the musical greeting card range that have discs in them that play a tune? Do you think, for those making music themed felted bags..anything like that would be feasible? You could certainly make a wee pocket for it to sit in but how to action it etc..?? Would be intriguing tho.
These musical 'buttons' are available from several crafting sites. Typically used for inserting in children's toys to play a tune, but I think would work for what you've described....(you'll have to scroll down to find title listings)