My wife has a 52cm Ruby with 105 components. I have a 58cm Roubaix with 105. Both are triples. When she is in her middle chainring and the small rear sprocket she gets a predictable but irregular "ping" that took a long time for me to figure out. It turns out that the chain is -just- hitting the outer chainring where the chain ring has small, circular metal tabs that protrude inward. The chainring has small circular metal tabs (four of them) in the area -just- below the teeth. If the crank arm is set to 12 oclock the tabs are at about 2, 4, 8 and 10PM. There is another set of four tabs that are in a circle just inside these outer tabs and just past the outer tabs so they lie around 2:30, 4:30, 8:30 and 10:30 oclock. Those tabs protrude to the inside of the chain ring but don't touch the chain.
The problem doesn't happen on my bike, probably because of a slightly longer chain stay? I have always been pretty anal about my bike being silent and have imparted that sense to her... so this is a bit of an irritant. Shifting to the outer chainring and moving up three cogs in the rear gives her virtually the same gear admittedly but it's an irritant. I'll guess a .5mm change would be all that's needed. Can a thin shim be added to the driveline side to push out the chainrings? I don't want to go crazy on this...just looking for a reasonably simple solution if it exists.