syn at times can make a motor louder...lot of harley owners I know and mine also seemed louder with syn oil..many harley riders and mechanics dont use straight syn ... and the dont use motor oil in there tranny or primary ..harley went with using there oil in all three holes for one reason ,,,because they where loosing money from people going to other brand motor tranny and primary oils....they people who are new to harleys and dont know better use the same in all three holes...thats why there loud and shift with a clunky sound...your missing out on a smooth quiet ride...someone mentioned metal shavings on there magnet drain plug...dam right the oil it to thin.....there not a race bike or race motor its a harley put together with lose tolerance..thats why they sound the way they do...right tranny primary oil once a year is good enough and can go longer if you needed to