Have you tryed just replacing the Diff fluid , sometimes that can help. I don't think you can get parts to replace the pinion bearing from Pontiac , that's why they are replacing the whole pumpkin. I want to say all replacement Diff parts also come from OZ. The gear ratio has nothing to do with the whine , if any gears are not set correctly they too will wear improperly and develop the dreaded whine. If you replace the complete Diff (say Kaaz) with 3.91's for $2000
then you may not have the Dana Whine , but from what I have read the Kaaz is not totally noise free - its just a much better LSD and 3.91's really add to SEG's. Hope that helps and Good Luck...