Gents,
Just bought a heritage, used, and have had this rattle driving me crazy. I found out it is the shock mounting bolt washers. There is a space between the bolt head and mount and the washer is rattling around in there. You would think the bolts aren't tight but first indication is they are and the bolts are too long and bottoming out. Anyone experience this? Thanks...

 

Just spray on the mounting bolts with WD40. Sit and bounce a little then spary some more. THat's what I did and it's gone. It might come back again when the WD40 washes off but I can always spray anytime. It's also a good rust protection. My .02 cents.