Our 2004 Navigator has developed a pronounced clunk, which is reproducable if you're driving at highway speeds and let off the gas and coast for 5-10 seconds. Then when I step on it, I feel a clunk, almost as if gears were engaging. I'm pretty sure it's the rear, this happens in 2WD (haven't tried it in 4WD mode).
If I accelerate gently, it doesn't make the sound. I'm somewhat mechanical and for those who are familiar with Volvo Outdrives, it's a similar clunking noise when they engage into gear.
I've worked on Volvo's for years, but I'm just not familiar with Ford products and SUV's.
I'm thinking either suspension or in the differential. Any thoughts or ideas ? The car has 98k miles on it, and has generally been taken care of.