Just recently bought my 2005 1600 Classic - I love this bike, but I am having a problem with vibration in the seat. Sometimes when I ride it is perfect - then other times, I get a very bad vibration in my seat. It is very annoying. I can usually correct by adjusting speed or moving in the seat. My previous bike never had any vibration. I have 2 friends with Vulcan 1500s and they have no vibration issues. I called the dealer and they gave me the old "we´ve never heard of that happening before". Before I take it in, can someone give me some insight on what might be causing this so I can bring it up when I drop it off? Any help would be appreciated.