I have a 95 heritage with 12k miles on it and when its real hot i have a rattle from the engine that sounds like an old car with spark knock thats the only way to describe it. I run premium gas and semi syn oil
The only mod i have are vance and hines straight shots with the baffles in.Its full of oil and only does it sometimes.

 

If it's only when the motor is really hot, it is probably a pre-ignition due to hot spots. Either carbon deposits or a sharp edge on a valve, piston or head may be heating up to the point that it can fire the fuel mixture before the ignition spark.

 

I agree!
You might try some UL100 race gas and run it for clean up or get some Upper Cyl Lube from Lucas, which will clean it out...my penny's worth.
Check your plugs too, they tell a story.
Right now your motor is talking to you, pay attention and find the problem, before she really gets mad.

 

retard your timing. mine did that after i had a shop adjust the valves and set the timing, they said it was normal. idiots.

 

Harley sells a fuel additive at the parts counter. Comes in small bottles.....each bottle will treat 5 gals. Drop one in at each fill up in the hot weather...........It stops the pinging for me

 

1/4 can of Sea foam in a full tank. 4 tanks & your sea foam is gone. It should take any carbon out of your engine, lube your top end & clean your fuel system too!
Hatch.