Don't forget the other favorite excuse from the MoCo and it's dealers; piston slap due to the short piston skirts (or the out-of-round barrels, but they don't talk about that).
I don't know that any one thing is going to make these engines quiet, and I also don't think you can assume that when one person claims changing lifters in his bike quieted the noise, for instance, that you will have the same results if you also change lifters. There are too many variables involved, and unless you want to spend limitless amounts of cash chasing the holy grail, you will eventually reach the point where you accept the fact that these engines are noisy. The CVO103's were relatively noisy compared to the 88's, and the 110's seem to be even noisier than the 103's. A lot of the theories seem to make sense, like the heavy valves and high pressure valve springs overpowering the stock lifters and oil system, piston slap, thin cylinder walls due to the cheap method of creating the 110 cylinders that are dimensionally unstable and are also unable to effectively dampen noise, etc. H-D surely isn't going to tell us, assuming they could figure it out, what the answer really is. Individual owners aren't going to be able to do it either. Perhaps someone with lots of money and lots of time in a fully instrumented engine dynomometer lab could in fact trace all the various noise sources and assign values to each, such as 30% valve train, 20% piston slap, etc., but I don't know anyone who is likely to volunteer to do this.
The secret, IMHO, is to figure out what really is "normal" for this particular engine, and then learn to live with the "normal" sounds and only worry about the "abnormal" stuff that will eventually surface. Next time you decide to buy a motorcycle, remember all this stuff and all the lack of help you received from the MoCo and your dealer, and then remember that old adage about doing the same thing over and over and expecting different results.
Jerry