I was once doing candid people photography in a public place with two friends. They had point-and-shoots and I was carrying my Pentax DSLR. After I took my first picture and the rather startled subject gave us a weird look and walked away, one of my friends turned to me and said rather angrily "can't you turn that noise off?!?!"
We had a good laugh at his expense, but the real irony is that he now shoots a Nikon FM something or other. I think you should learn to embrace the noise, since it comes with the territory. I would never seriously consider shutter sound when buying a digital body unless I needed a really irrelevant tiebreaker. I suppose I would maybe mention to my clients that my professional-style camera will make professional-style noises, because if they'd rather have me use a point-and-shoot I would rather not work for them in the first place.