It is not THAT loud really, it is just more accented tap/ slap. Try to read the review of D200 on dpreview and listen to the shutter sound.
It sounds the same "loud" and "pronounced", required probably due to durability and speed for 5fps. D200 is louder than D70
The 1D shutter sounds are quite noticeable too.
I realised that the cameras that do 3 fps have softer shutter sounds eg. 300D, 350D, 10D, 5D, D70, D50.
Anyway I have managed to try the 30D shutter sound, it is really NOT that loud, a good improvement really. Tried 30D and 350D side by side, both volume are about the SAME, it is just that the 30D shutter sound is lower pitch, of shorter duration and more punchier, accentuated (or what some people which may "violent"), hence giving the feel it is much "louder". 350D shutter sound is more higher pitch and more "gentle" and "slower", hence giving a sense that it is "softer".
Just dont worry, if you want either cameras, neither shutter sounds will be deal breakers IMHO
The 30D is tempting....