To be clear, if I thoroughly clean and degrease the chains, let dry, then apply something very viscous like Finish Line Wet Lube and wipe dry, the Di2 is nearly silent. For a while. But dust and road dirt are really attracted to that viscosity of lube and start to gunk up the chain, even if I wipe after every ride. Since it's not a one-step lube like RNR, I have to clean, degrease, and reapply.
The RNR Gold, which is a dry lube but also an all-in-one cleaner + lube, is much easier to apply but doesn't get the chain as near-silent as the wet lube. This has been true on my 2 Di2s and eTap. I'm hoping the SCC Slick will give me the performance and silence of the wet lube, with the lower maintenance associated with the RNR. If it does, it will be worth the $25.
The reasons I believe it's not an alignment or setup issue (aside from the fact that I've had two techs from two different LBSs check it out) are 1) that it's dead silent when applying the wet lube, nearly silent with RNR, and slowly gets louder as dirt accumulates...if something were amiss it would make noise all the time, and 2) shifting performance is exceptional (and yes I know how to microadjust both Di2 and eTap and have dialed it in when changing out wheels). It's a common pattern. Lube it, it gets quiet. Ride 30-50 miles, it gets louder around the 40-50 mile mark. Again, SoCal is a very dry and dusty place, so my riding conditions may be very different from yours.
What boggles my mind is how quiet my 105 stays because I don't give that the same level of care and attention. I think there may be something to the theory that chunkier/lower end drivetrains being more forgiving of dirt/grime due to not having the same tight tolerances as higher end drivetrains.
Also, not sure if linking to Weight Weenies forum (which I'm not a member of, but when I was doing a Google search on the noise I came across it) is allowed but there is a thread about Di2 noise, so it's not that I got the 2 bum sets in the lot.
