Sound is normal, its the primary chains rattling. it will get a little better once you get it running right but you will always hear it. By the way the rpm hangs when you rev it , its still either really lean or the ignition advancer is not working right. With the problems you keep finding with the carbs I would tear them back apart and clean them again. Seems like you have stuff still plugging things up. Also look into putting an inline fuel filter in there to keep debri from the tank going to the carbs. I still wouldnt count out a vacuum leak either by the way its running.