Low RPM chain type rattle

My '80 is using a stock tensioner with a "back-up bolt and nut".  The current project I'm working on came with a ZX-11 tensioner.  The "heavy duty" spring in the ZX10 tensioner was removed and replaced with a "lighter" one.  The "awl" was removed and replaced with a small piece of brass tube.  The piece of tube prevents the "plunger" from merely falling out.  The end cap was drilled and tapped for the back-up bolt and jamb-nut.
In my opinion which is based on some common sense and over 40,000K on the similarity modified OEM in my '80; It's less about the tension(pressure) that the tensioner applies and all about having the minimum chain-slack to prevent chain-skip.  The lighter spring maintains some contact between the Rubber Roller and the chain via the tensioner and equally significant - eases the wear on the Nylon Sprocket if it's still being used.  A back-up bolt is required for obvious reasons.
 

My 79 is doing that now too. It runs an APE cam chain tensioner which I checked and at low rpm rattle is still there. Engine relatively fresh, I bet it has less than 10k mile since complete rebuild.

My CBX got me to thinking. When I did a synchronization of the carburetors, I purposely made them go way out before performing the adjustment. When the synchronization was not good, even the Cbx had rattle noise. And the Cbx much much much smoother than the KZ 1300.

Which got me to wondering, if maybe a bad synchronization puts different pulses into the crankshaft which causes any one of the internal chains to become noisy?
 

That may be something I check on mine as well. My bike has DFI which is 3 sets of 2 barrel throttle bodies. I would assume these would need synced. The bike sat for 3 years in a hay barn before I saved it from the scrap yard. So thing are a bit sticky.

I will let Y'all know my findings I just have not had the time to dig into it yet.

My rattle at idle noise turned out to be loose Sprague starter clutch..