One problem related to loud engine noise has been reported for the 1998 Lincoln Navigator. The most recently reported issues are listed below.
I drove from maine to mass. Approx 170 miles, we stopped at my boyfriends mothers house for 20 min. I got back in my car started it up and it had a horrendous noise under the hood. It sounded like a motorcycle was in my engine. I did not feel safe to drive it anywhere. We had to have it towed home and our mechanic told us the bad . . . Awful news and the expense. I have a blown spark plug and need a helicoil resulting in a new motor or mine being taken apart (which one is cheaper) I am a single mom and cannot afford to replace the part as I have a $350 a month payment on this vehicle!!! fortunately this happened while we were parked and starting it up and not somewhere on the mass or maine interstate. Contacting Ford hasn't worked, I just got a generic email acting like this is news to them yet I can find documentation all over the internet from people with the same issue!!!!.