The chain length seems ok.
However, after testing a bit more, I found that the vibrations are there even if I stand still with the clutch pulled or with the gear in neutral. When riding, I usually notice the vibrations when over 4000 rpm. Really noticable at 5000 and really annoying at 6000 rpm.
I now found that if I stand still and rev the engine, I can actually feel the vibrations at 3000 rpm. Going past 6000 rpm just seems to increase the vibrations.
Also, I suddenly remembered that when I replaced the spark plugs last year, I also replaced one of the spark plug boots with a new (Suzuki OEM) one because it wouldn't sit snugly on the spark plug. This got me thinking. If one of the spark plugs is not firing as it should, could this be the cause of vibrations?
If so, how can I check that they all work? I know how to check spark plugs on one cylinder engines, but there are four spark plugs on my V-strom. Should I just remove one at a time and try starting it while checking for a spark? Is this doable? Also, they are not easily accessible (need to lift the tank, etc). Is there an easier way?