Hello Alex,
welcome to the Stridaforum!
Bartman236 meant part nr. 363 (367).
Actually this is not a washer (like part nr. 364), it is a disc (or cup) spring.
Please read more about that here:
[url]Broken 373 Bolt]
[url]18" Wheel Upgrade: not that easy...]
Once again, thanks to Bartman236:
I’ve skipped step 1, because both of my Stridas were “as good as new” (50 - 100 km) as the noises started (and the burrs were not deep).
The sharp edge at the outer diameter of the inner side of the ring.
First I’ve tried silicone grease, but it doesn’t last long.
Much better is this:
http://www.neverseezproducts.com/bostik.htm
The noises came back on the black Strida after riding ~ 700 km, this time I’ve skipped step1 and 2.
Applying of 1 or 2 cubic millimeters never seez at the cup spring edge killed the noise again with less effort 
Further questions are always welcome.
Best regards
BSA