mmm the sound rather irritating lol!!! my brother in law has a 35mm same thing but his louder, he brought it back to NSC they say its normal, but he insist that it just sound not right.., well they accepted it and return it back to him in a couple of days, at first no sound the normal shoom...shoom sound and then it starts again... it sounds like the something circular scratching metal, errr issit due to lac of grease?? lol but i read around the lubrication dun dry off easily..:think:
I am wondering, could it be the sound from the VR? Try turning off the VR, and see if the sounds are still there.
Also, in any DSLR, there will be some sound from the AF. In quiet moments, it will appear to be louder. And once you notice it, you will strain to hear it and it will appear even louder and louder. You cannot expect it to be as silent as a PnS. One side note, my old 18-55 and my curent Tamron 17-50 sounded pretty 'loud' and obvious too. But I have been around older film cameras, which are many times louder, IMHO.