The extra noise has two causes. Third-party lenses often have a two-part action to move the aperture blades, because the action has to be adaptable to other camera mounts. A Pentax lens doesn't have to be as flexible so the design can be simpler. In a Vivitar, there's more stuff to rattle around.
Also, this is a telephoto macro lens, so the aperture blades are pretty deep into the lens. If you're focusing really close and the lens is fully extended, those blades are about 2" deeper than with your 50mm prime. These long metal arms are what moves the blades: