Some metal bodied cameras tend to resonate and amplify the shutter sound. I've had it on Nikons, Canons, Yashica, etc. Pro models like the F1 seem to do it less because of better damping but none are completely immune, although I never recall my OM1 pinging. Some audibly ring for a few seconds afterwards, which can be irritating. Plastic bodied cameras are less prone, generally speaking, to the dreaded ding. My theory is the pressure plate acts as sounding board for the stop down lever or mirror mechanism. Film tension damps the springs in the plate, reducing resonance. If it's any consolation, some rangefinders are equally subject to shutter ring.