Interesting -- I know that the color dial postwar Contaxes can have a noisier shutter because of the flash synchronization mechanism
This is not true. What can a postwar "color dial" Contax IIa / IIIa shutter do is to refuse to fire when you depress the shutter release button, and this is quite a consistent and pesky behavior with a large number of those "color dial" cameras, for some X-sync design issues (to sum it up, the X-sync circuitry is oddly incorporated into the shutter release mech., just under the shutter release button, thanks to a very complicated design and not at the end of the shutter curtains journey, like with normal people). But the shutter is absolutely identical to the "black dial" shutter, for all fast and slow speeds. So it cannot sound different. No way.
The prewar Contax shutter definitely makes a quack which is more or less perceptible depending on the condition of the shutter and on how it was adjusted. A clean and properly tensioned shutter will have a reasonable one. If the camera quacks to a point that it shakes when the shutter fires, yes it's likely because someone overtensioned the 1st curtain drum roller springs unit, at the risk of breaking that precious part sooner or later.
An overtensioned Contax II shutter usually provides high speeds which are way too slow actually.
Don't expect a prewar Contax shutter to feel and sound like a Leica M shutter. Never ever. A good postwar Contax shutter can be noticeably quieter than a screwmount Leica shutter, while not being totally as quiet as a Leica M shutter.
A Contax II and a 1951 Kiev II must sound and feel identical at all speeds.
I have looked at the OP's photos made with the '36 Contax II on his flickr and there is nothing wrong which I can see on those scans. We should have hi-res scans to compare with what he gets off his Kiev II with the same lens in front of the same subject (camera on a tripod, same lighting conditions, same distances, same speeds) to see whether there is something with that camera shutter which brings abnormalities on the photos.
But my guess is that we won't be able to see nuffin'. There are some spherical aberrations in the OOF areas of the photos and particularly in the corners and particularly on the #1 pic but those are quite expected from a prewar Sonnar. But the exposition is even, there is no strange vignetting, and nothing telling about an unexpected optical or mechanical problem. Fomapan 100 is very tolerant to overexposure error so we have no clue there about the high speeds being in the good ballpark or not.
