If there is no evidence or proven history of an overhaul for this camera, the first thing to do would be to check exposures, using slide film. This narrow latitude of slide film will highlight obvious exposure errors even of simple, uncomplicated scenes very readily, making it much harder for the camera's electronics to proverbially sweep niggles under the carpet.
Shutter capping can be a problem (often as a result of the camera sitting idle for months, if not years), but it is not as prevalent as with the earlier rudimentary Pentax 6x7 / 67 cameras. Shutter speeds are best tested electronically (by a test facility), not "by sound". Many things can be wrong, so a very thorough look-over, in and out is definitely required, and have your Plan B for returning the camera to the seller if things do not shape up.