my 96 seville has 2 shift solenoids that like to fail. they can be replaced without dropping the trans. I know the GP buzzes at 10mph. sometime it does, sometimes it does not. I am going to check the cat. heat shield. the trans guy i talked to said the shift solenoids are under the side cover. big pain to get too but less $ than pulling tranny. the seville has the 4T80E trans. supposed to be rock solid.