I previously reported that my March 2013 copy of the 24-70mm (serial number beginning 032) does not make a clicking noise when zooming. I've been using my lens as usual for about 6 months, but all these additional reports got me checking my lens again.
After many tests in a completely quiet room with my ears right next to the lens, I report that I can hear a very faint single click sound as the lens barrel expands past the 50mm mark (like a tiny spring or the inner cams moving into place). This sound is really faint -even the zoom ring moving is louder-, and it takes moving the zoom ring very slowly to even catch it. This is not what you guys are talking about, right?