Actually that is pretty common on the 1200's. Some bike do it some don't. I've had 3 1200's and only one of them did it. Usually I notice it after sitting at a red light then I pull away and about the time I hit second gear it starts rattling. Only last 1 to 3 seconds or so. I was worried about it at first but since then I've learned that some of the 1200's do it without any apparent bad effects, other than the noise, so I pretty much ignore and expect it. The 1200 was honda's first foray into hydraulic lifters and I think they got it right on the 1500. Maybe not as they went back to mechanical lifters on the 1800.My valve startsoff q.uite after riding a while left side has loud taping sound that comes and goes I have replaced lifters and shimed to spec also gauged rocker arms. When noise starts I let off throttle AMD noise stops for a while
I do know that the more I ride the 1200 the less it does it. So the real "fix" for the noisey valves is to ride it more!