I have a major hunch that the MT-90 is the reason why people are having issues with the 98 spec transmissions and highly recommend running MT-85 instead. While I don't necessarily think it will cure the issue completely, I'm wondering if it obviously reduces the noise to at least indicate it would be the right way forward on a new unit. I don't think anyone with a whining 98 spec has posted results from a fresh fill of MT-85, it would be a great data point to have if you're willing to try it.