Check all the front motor mount hardware, my 06 is a little diffrerent with the single front motor mount but I completely lost the nuts on the adapter plate between the motor and the mount, sounded like my bell was ringing from motor vibration.

 

I had the same issue on my 2010 street glide, drove me nuts. It was the top engine mount right behind the frame down tubes. Spray some lube on those ball and socket ends of the mount and see of that stops it.