You are proly right Tom! I think I got two bad ones in a row....makes sense to me as I bought them at the same A/Z store.
I'll just add this as another "shot in the dark". Both of the black M1's did the same symptoms: more & longer rattle time on cold start up, which to me is 5 - 7 days of sitting. A small amount of rattle on hot start ups, again to me is any start the same day after cold start up. And the bonus symptom, my O/P gauge was taking it's sweet time to show pressure on any start up but markedly on cold start....I was starting to think the sender was checking out.
Last week I swapped in a Bosch 3401 and this past Saturday's run the rattle on cold start was back to 3-5 seconds & not too loud and silence on hot starts and my "maybe going bad" sensor suddendly came back from the DNR list. I'm stumped because the grey M1's didn't behave like the new black M1's.
Tom