you seem to be getting wastegates and dump valves mixed up. They are totally different things and do different jobs.
Wastegate is to control maximum boost, it allows exhaust gases to bypass the turbine wheel at a set boost pressure. It's controlled by the wastegate actuator which on older cars is nothing more than a diaphragm and a spring, the strength of the spring and the preload you set it to by adjusting the rod length control the pressure the wastegate opens at. On more modern cars it is ECU controlled using an electronic valve which opens the wastegate when the ECU sees fit.
A dump valve goes on the boost pipes after the compressor of the turbo. It is there to stop boost pressure spikes when you lift off the throttle and the turbo is still spinning. It does two things, one is to stop the compressor from stalling in gear changes so you are on boost quicker when you floor the throttle again as the compressor can keep spinning. The other is to protect the compressor wheel from boost surges that happen in the high pressure side when you close the throttle suddenly. This can fatally damage the turbo. Generally speaking, if the manufacturer of the car the turbo you are using came off saw fit to use one then you should too or your turbo might not last very long. It can and has wrecked K03 turbos. If you don't like the noise then simply fit a re-circulating valve which dumps the air back into the low pressure side of the turbo instead of to air, even my volvo TDI engine has one of these, most standard turbo engines tend to.