About 2 months ago, I noticed a light ringing noise when I was unfolding my Evo3 to ride, and traced it to the lockring on the beltwheel, which had come loose and was hitting the crankarm. I managed to carefully screw it back on using a pair of small finishing nails to handle it by the slots on the edge.
It’s come unscrewed twice since then, and I’ve screwed it back on each time. Is there a way to keep it on better? Is this possibly an indicator of a larger problem?
Well, I think all you need is the right tool 
The internal lockring of the KS3 should be tightened with a torque of 50 - 60 Nm,
guess two nails are not able to achieve that torque. You need a hook key Ø 95 mm.
Once again, at this chance; the belt tensioning method shown in the Strida manual (without using a hook key) is definitely wrong!
I just realized that the part I’m having trouble with is called the DRIVER lockring (HSL974)!
If I tighten it down too much, hard pedaling will sometimes torque the whole of the KS-3 assembly, over-tension the belt, and seize the whole system.
If I don’t tighten it enough, it works free and hits the crank, while also allowing the front beltwheel to slide out to the edge of the splines and drop the belt.
I think need to ensure that the INTERNAL lockring is tight enough to stand having the DRIVER locking property tightened (and maybe just walk up certain hills…)
I wonder how that could be possible - the locating block’s (HSL976) function is to avoid just that!
Is the block missing at your bike?
I don’t think so.
First, you need to tighten the driver lockring properly - and you need an electric (or pneumatic) impact driver, next to the special nut, for this task.
The locating block and the big groove nut together should be able to secure your drive against unwanted rotation without any problem.
I don’t think I actually have a locating block - the only parts on attached to the KS-3 are the kickstand bracket, kickstand, and the bolt that holds them together! Looking at Bill’s handy pictorial guide, I just realized what that part looks like, and that since I can see the ridges where the locating block should be, it’s definitely not there.
Likely it got lost when I had a bike shop swap the KS-3 when when the original one locked up on me a couple years ago.
Any idea where a replacement can be had?
Wtf? 
Well…I’m afraid that will be a problem…no idea where to get this thingy 
Good question, but I have the answer as I do have some extra parts. Please contact me through my website and I will add the part to my inventory. stridacanada.ca/
Cheers, Bill