I think your camera is normal. The loud sound actually comes from 3 sources inside the camera, and as you said they are all mechanical ones:-
1. Mirror up and down;
2. Shutter opening and closing;
3. The movement of the mechanical aperture coupler and interaction between the couplers of the lens and the body.
THe DS actually has a virgorous mirror action of which the mirror sound is large. The real bad effect is that this also cause more camera shakes. When compared with the *ist D, the *ist D's mirror action is much gentle and smooth.
IMO, the shutter sound of the DS is not very noisy.
Finally, it is interesting to note that the aperture coupler sound characteristics will vary with different lens mounted.