I have a 90 420sel with 132k. I have had the timing chain done about 22k miles ago. I do have a little noise from the lifters that has been there for a little while. the other day, I noticed almost a knock in what sounded like the front of the engine. I revved the motor and it did not stop. I pulled it into drive and it quit. I never heard it again that day. Then the next day I heard it again and through the same procedure, it stopped. Can anyone tell me what this might be or if I am looking at a major repair?