The shutter noise of Contax II and a Kiev 4 have almost the same level and pitch. There is a difference in the noise (re. other FP shutters) as the curtains in the Contax/Kiev are very slowly moving at low speds, but the escape movement can be heard (whirling sound). This noise can be annoying to some people when background noise is low or null. At high speeds, the noise is still very low and can remain unheard as long as some room noise exists. It is a low freq. pitched noise, very short in duration, which is always less noticeable than a high pitched one (I think it´s at least less disturbing). Campared with SLRs, (with mirror locked up), the noise level is slightly lower.
The Canonet QL17 and New Canonet QL17 are very quiet cameras, as well as the Yashica Electro 35, but their shutter noise is more metallic and higher pitched than FP shutters due to the small size of leafs, and because FP shutters curtains made with rubberized fabric, act as noise dampening devices.
I´ve been using all those cameras for a long time, and unless the room was silent, no one noticed I was shooting.
Ernesto