My 97 Diversion 900 developed a resonant thrum at 23000kms. Sealing off the fresh air entry tube to the exhaust (emission control requirement for US) reduced this but it is still significant. Happened quite abruptly on a particular ride. Been getting more noticeable since then. Associated with the thrum is a fine vibration throughout the frame, annoying to have it in the throttle hand. More harsh blatty sound went winding it out hard. Bike still has same power, same fuel economy, engine seems quite sound. Wish it were like it was when I bought it – it was like flying. Little less than that now. Any help out there anyone?