I have a new rattling sound @ about 3000 rpm when the bike isn't at full temp. It seems to subside or go away fully warm. Any ideas?

 

I failed to give some details. This is a 2004 FLHT with the stage II kit with thunderheader & 203 cams.

 

Well you can try a few things, first off piston slap is the first thing that comes to mind. Warming a bike up before riding is very important will allow many more miles from a build.

If you start the bike dead cold let it warm up till the cylinder is hot to the touch does it make noise?? You could also have a lifter starting to fail. Both common issues.

 

Sounds like an external rattle, possibly. Heat shield, exhaust bracket or something a little loose that tightens up when it's up to temp. Lot of stuff on an FL and it only takes one thing a little loose or out of place. My TourGlide fairing rattles like it's falling apart below 50 degrees - over 58 and it's quiet....