This has been an ongoing complaint with later model Harley owners.
In fact from around '08, lifter in the CVO 110" motors can let go with just a few thousand miles or up to around 20k miles. They all seem to derivatives of GM hydraulic roller lifters, or at least their design.
I have 20k on my '09 110" motor and I'll be changing out my lifters this winter just as a precautionary maintenance.
But what really makes these lifters sing is the cam profiles. You would not believe all the different ramp angles, durations etc that make them either quiet or noisy. Obviously if the ramp angles let the lifter roller to come off the cam you're going to get a bit of clatter. One of the reasons the lifters go out so often on the 110" motors is the VERY stiff valve springs. If they loosen the pressure the lifters last longer, but make noise...
I would think in the case of the S&S motors is that it's the cam profile that creates the most problem, not worn out lifters. But anything can go south even when new.
Just some thoughts from a rambling old fart without a M3W.
