Since the early days of owning my Rocket, I've noticed a little rattle (or buzz) that occurs under load around 2500-3500 revs. Giving the bike a (literal) spank on all the parts when on the stand, I found the front mudguard to twang when knocked. So I got my dealership to take a look at it, and a tech reckoned he could put a grommet somewhere on the mount that should resolve it. So that happened last week, and I rode home looking forward to a rattle-free ride, only to find that it wasn't cured ... if anything it may have gotten worse somehow! Having then taken my life in my hands to try and feel around the bike when riding in 1st at around 3k revs, I think I've discovered the true culprit! If I place my hand on the left headlight, the noise stops!! But when the bike is stopped, nothing seems to be loose, or rattling about the headlight casing. Just wondered if anyone else has had this, or anything similar, and how to proceed - other than to go back to the dealer again, and have them try to deal with it.
Try holding this part(s) and see if it stops. I have the same problem and think I have narrowed it down to this.
