Check the basics first. Pull off your clutch cover and inspect your clutches, basket, etc. Second if all is well, check your shift shaft adjustment and eccentric screw. These come out of adjustment all the time. Sometimes they were not installed correctly, sometimes the retainer washer fails, either way - look into the basics before you split the cover. A friend of mine had a "squealing" noise in neutral once - sounded bad. Pulled the cover, shift shaft was waaaaay out of adjustment, his eccentric screw had backed out and would not allow the trans to fully up or downshift.