04 Fatboy with only 4900 kms, bike has been running great until today when stopped I heard a rattling noise from the primary side of the engine. I drove off and the noise disappeared but the noise comes back at idle but no noise when the engine is under load. Where should I start looking??

 

You could check the compensator nut, but that would almost sound like an engine knocking. give a good look over all the external parts like motor mounts, belt gaurds, chrome trim to eliminate the simple stuff first.

 

First go over the whole bike with a wrench. Check your jiffy stand to see if it is hitting the frame.