I recently completed a 4000 mile trip from Canada, through the US southwest and home. There were 4 Ultra classics in our group representing model years from 2007 to 2009. We all experienced a lot of engine rattle under load when using the US 91 octane gas with 10% ethanol. Even adding octane boost did not eliminate the rattle although it did improve things a bit. Once we got back to Canada (no ethanol) things settled down. So, my question is: do you folks in the US experience this engine rattle and is there a fix that will eliminate it? I do a lot of touring in the US and would like to know if there's something I can do to eliminate the problem the next time.