rattle noise comes and goes with throttle position?

wow this is driving me nutts, 1983 750 maxim, has a loud rattle(almost like a knock) and i can make it go away with simply backing off or adding throttle... crazy huh!!!
in the shop on the stand it wont do it even in gear!!!!!
you have to be running down the road and its most prominent at about 4200 and up
under 4000 its dead quiet!!!!!
bike runs like a swiss watch, zero problems, smooth as glass......
is this normal intake noise im hearing?
gets more noticable when the bike has been run for about 50 miles and is good and warm
ive pulled the valve cover and all looks good there ,chain is tight and cams look new
i got this bike last year had 5000 miles on it it has 19000 on it now and has always had this noise
im stumped and i dont want to dig into an engine if i dont have to
has anyone ever had this mentioned before?
id appreciate any help on this
thanks

 

Driveshaft joint ?

 

The sound of cam chain whizzing?

 

perhaps an exhaust leak on one (or more) cylinders?
I have an exhaust leak on number four, right where the pipes meet the engine. It causes a loud clicking at low rpm, and when i'm really pulling the engine hard, but goes away under normal riding at higher rpm or coasting.

Although if it were an exhaust leak, you should be able to hear it on the stand in the garage, just a thought...

Can you tell what part of the bike it's coming from?

Does it get louder when engine braking?

 

like i said it does it at 4200 rpm and up ,and when the bikes planes out..
like ya get to 60mph and the bike is planed out, level road (better described as satisfied) the rattle is there

all i do is add throttle or lessen throttle, the rattle dissapears,until it planes out again , then the rattle starts again, crazy huh!!!!!

thats why i was thinking maybe air box noise ? or am i hearing somthing else?
i have leaned down at speed as far as i dare to try and pinpoint the source,
but havent had much success (passing motorists have gave me the look wondering what are ya doing ya idiot)
i had the valve cover off the chain and cams are fine
i dont know enough about this bike to rip into the engine
dont trust any local shops enough to let them do it either
just curious if anyone else has had this noise with this model and year bike
and is it normal ?
thanks for the response guys

 

i had the same problem with my truck it was the u joint

 

Center section (collector) of exhaust system have something loose inside it?
i've seen it before on these bikes.

 

Mine vibrates some right at 4500 RPM. It used to do it quite a bit, but it did it less when I switched to mid-grade gas. It did it even less when Don synched the carbs. Still does it a little though. I don't think anything is loose on the engine or headers. The bike runs nicely other than that.

 

Mine does that at about 62 mph and stops at 68 mph anything below or above no problem I did some more carb tweaking today (got more power low and mid) maybe this will help mine I hope other than that I do not stay in that range long. (fith gear only)

 

If you are runnig cheap gas it may be spark knock. I only run 93 or above. but you would hear it on low end or shallow shifts. it is a idea.

 

I had a loose heat sheild on the exhaust. It went away when it fell off on a spirited highway run. OOPS. Sorry.

 

mine does the same at the same rpm, using 91-94 octane depending on what's available.