Interesting ref the filter. My bike has been sounding loud for ages but I sort of got used to it and just put it down to the highest mileage. But I decided idea to check my crazy know nut after reading this thread. It made sense to me as my 450ktm did the same but I never put two and two together! Anyway this week I had some time off work and pulled it apart to check. Yep nut was completely lose with tab washer holding it in place! Fixed it and took it for a spin...... wow so quite now! It's amazing what you can get used to over time. Only iffy bit about the job was having to wait for the inner clutch cover gasket to be ordered in. I phoned every yamaha / aprilia dealer for miles around looking for one in stock but no luck. Amazing as it's a common engine .