The lens on my nikon d90 is a 18-105 VR. Everytime i press the shutter release half down it makes a small cliking noise, then a second later it makes it again, if i hold my finger on the shutter release it will make it but if i carry on holding it the second click wont come unless i take my finger off. It's only very suttle, and may just be how the lens works, it's just slightly annoying.