Engine knocked on cold at first when new, then as time went on, all the time. Oil level was good, as was oil pressure. Dealer first told me these engines (Northstar 4.6) only knocked when cold, and quieted down when warmed up. After about 15k miles, it would knock intermittently at any time. Dealer (and you have to know a GOOD one) indicated that the repair was a replacement of all cylinders (and several other internal engine items), covered under warranty. 3 days later, and now 10k miles later, no knocks!