Transmission Rattle?

HI all.  My 79 KZ1300 runs like a champ but I've started to hear a rattling sound when the bike is in motion.  At first I thought is was something plastic (sounds that way) knocking around under or inside the fuel tank, but nope.  It seems to have nothing to do with the engine since I can run and rev all day with no rattle but when the bike is rolling I can hear it, even rolling slowly on smooth concrete.  

Does this sound familiar to anyone?  I'm wondering is maybe a piece of transmission broke off and is knocking around somewhere. I did a garage clean out recently and have to find my manual.  At this point I don't even know how/where to access the transmission to inspect it.  Can anyone point me in the right direction?  Thanks and be well.

-Michael

Tough one to answer without some history like how long have you you owned the bike and how many miles/kilometers on it. Engines that have a "rattle" going on inside shouldn't be run unless you are trying to blow it up. I had 2 cbx's over time and they had an inherent issue which the generator drives that made them rattle at just off idle. The KZ shouldn't rattle.
The cam chain tensioner- You really need to inspect this item by taking off the top valve cover and looking down inside. There is a nylon toothed gear which have been known to disintegrate if the tensioner was not taking up the slack in the chain. 
Also located below the nylon gear is the tensioner roller which is a black rubber roller also known to disintegrate.
Primary and secondary drive chains Depending on the mileage may get loose enough to rattle off of the engine case. There are no take up tensioning mechanisms for these chains. They are replaceable. You can inspect them by pulling off the oil pan which can be a pig depending on your exhaust system but in any event, if you have an internal engine rattle, I would be pulling the oil pan. If something broke loose, it's probably in the bottom of the oil pan.  While you have the oil pan off, it's a good time to inspect the oil pump pick up tube screen and clean it. If any thing has disintegrated, the oil pump will try to pick up the pieces and the screen will be clogged with debris.

Good luck and let us know more about the history and what you find please.

 

Sounds like a nut/bolt/washer or stone is sitting on top of your exhaust......somewhere.

If I understand , with the Bike at a standstill , engine running , no rattle  noise , but on the move you hear a rattle , and you think it is / maybe Transmission . If you have a centre stand , can you have it running , and go through the Gears ? Bike on stand , have you spun the Wheels , could it be a loose brake pad ,  listened at the prop shaft joint . Checked all engine mounts . Could it be your Centre stand catching . Is it all the time when moving , or just in a certain gear .  . Could it be from your Speedo , or drive cable . Just thinking out loud what I would be checking .

I'll rephrase my response:

It could be something as simple as a nut/bolt/washer or stone, sitting on top of your exhaust......somewhere.  (From experience)

Depending on your exhaust - because you've offered no real info:- It could be a loose/ rattling part of the exhaust/muffler.  
I prefer to start with the "simple" ideas.
 

Did you ever determine the source of that rattle?