I also tried several sprays and lubricants as well as cleaning the belt and sprockets, yes they worked for a few miles but then the noises returned. The worn rear sprocket was the main cause of my problems, probably made worse by dirt pick up, as Gambalunga says. They don't make any noises from new, only after a few thousand miles which suggests wear rather than adjustment or needing lubrication. All is nice and quiet now and running well, touch wood.....
