90 420sel engine noise
 

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?

Are you hearing this knocking noise primarily during the warm up cycle?

Scott, did you ever figure out what the knocking was on your car?

Air pump?
 

My 420 was doing that, but only when started cold. Once the engine warmed up, as designed, the air pump no longer ran, so no more noise. I unplugged it, since my state does not test for emissions, and had no more problems.