Agreed, let's describe this condition a little better to the OP. I've likened it to a shaken coffee can with some gravel in it. I thought it was a knock at first myself.

I also agree to get the Krieger tensioner. I'm a fan. You mentioned dyno and stethoscope. Once the condition gets worse, you should be able to get the rattle with no-load revving and could diagnose. I hate to just recommend throwing parts at an incomplete diagnosis, but Krieger's product is good, inexpensive, and you'll probably want one in the long run anyway. I'd put $5 down that it'll solve your problem.

 

The cam chain has the very odd ability to rattle like mad between 5000 and 6000 rpm and then go totally quiet up to redline.

Since you are trying to avoid the high revs, you've probably not reved out of the rattle yet.

I just speed up or slow down to get the engine out of that rev range. It is a negative feature of our bikes.

 

If it sounds like a sewing machine then its normal. But the sound you describe may well be the ACR being rattled because the Cam chain is loose. But on a bike with that low of miles, something doesn't sound right. I didn't have noise till 5000 miles. Then a quick Cam Cain adjustment and it was gone. I don't have the manual adjuster, but it sounds like the bees knees.