I am a new owner of a 1800c. Little back story might help. Bought the bike 2006 1800C with 9100 miles about a month ago. I am a new bike rider, learned to ride on my old Shadow 750 last August. So I don't know the in's and out's of bikes yet. Wanted to upgrade to an 1800 and love it. Anyways, I bought the bike. Had the oil changed last week (not knowing when it was last changed, bought from an individual), had new Bridgestone tires put on it. Have rode it three times since changing the oil and new tires. The bike randomly makes a quick knock sound and vibrates the bike a little (can feel the vibration in my foot) doesn't shake the bike lol . Not a loud bang, but a knock. It randomly happens about once or twice a mile, then it won't happen for ten or more miles then another knock. I have never heard the knock while the bike was idling in my garage just while riding. I was afraid it may be something serious. Please help!!!