I'm new to this forum, and I'm curious of the outcome of your 06 CRF450 tranny. I had a very similar problem with winning tranny noise when warming up in nuetral. If up on stand the tranny would suddenly act as if it were engaged into gear. My shop tore it down and had a technician rep from Honda come and look at it. He and the mechanics had no idea, and recommneded replacing two gears and some spacers and clips, and charged me 1,200.00 bucks. When I got it back I added 2 oz. extra of oil over spec, not having a problem now, however, not sure if they fixed it or the added oil did. I heard about the oil in the forum not from Honda. Did they warrantee your problem?