Originally Posted by benjikan 
I was in the same room as my girlfriend and there was some street noise, but not excessive and I took an image and asked.."did you hear that?" she said "heard what"..."the shutter"..."No didn't hear a thing"..It freaked me out when I started using it. I think it is as quiet or more so than the Canon 400D...
Are you using the Live View? I can see why if you are using Live View with the mirror in up position. Just the shutter without the mirror flap would be very quiet indeed. But if you are using the usual optical viewfinder, then Pentax must have upgraded the mirror box in a big way.