Ok I just got myself a 97 gtp with 144k on it in didn't here the knocking when i checked the car out but now I hear it at idol. It's comeing from the snout but I feel no play in the pully. So I didn't know if it would be the coupler or not it sounds like marbles rolling around. They didn't know when the s/c oil was changed so i know that has to be done. But the noise is driving me bonkers now.