had the same noise from my 2002 280 pro i bought as a non runner for a lot of years, so decided to change the main bearings and seals but when rebuild and started it sounded like a bag of bolts and my heart sank but after i strip the clutch side off notice under close inspetion that the basket and crank gear had marks on them as something must of came loose at one time and causing the damage,got the dremel out and clean the damage up on the gear wheels the best i could and rebuild and started,this cut the noise down by half but now i know what to replace when i get the ££££££ in