Another T5 vibration issue

Hi all ... I have a T5 classic 94 , with Malossi 172 ..I have just changed the exhaust from a Rs scoot to a Sterling .. Very bad fit , but that is another story . Anyway sterling eventually on and noticeable vibration at mid to high revs ..Sod it ..purchased a sito ... Still vibration . Changed rubber engine mounts and shock and mount , no difference . Some have suggested flywheel bearing . Since the vibration scoot has done 300 miles or so and not getting any worse . But I have no confidence in opening it up for fear of it going bang .

any thoughts ?