OK, I have a 2005 4x4 2.3L auto escape. In 2008 the engine blew at about 65,000 miles, obviously out of the milage warranty as well. So I had a new engine and the tranny rebuilt at that time. Now I'm being told the engine is bad again, and again outside of warranty (5yr) and around 50k miles on it, 112,000 miles total for the vehicle.

But it seems odd that 2 engines in 112,000 miles?
Oil gets changed every 5k miles or six months, whichever comes first, and I use a name brand full synthetic and motorcraft filter. Believe me, after replacing the first engine this one has definitely been taken care of so theres no abuse of the engine to speak of; but to be clear the first one wasn't abused either.

When the engine shifts at higher rpms (3500 is pretty normal for it during average acceleration so a little higher than that brings it on) the noise that comes from under the hood is terrifying. When its parked and i slowly raised the rpm at almost 3k it does it. It sounds like suddenly something letting loose and vibrating/grinding and stops almost as soon as the rpms start to drop. The sound isn't high pitched, the best way to describe it is if you stuck a playing card in the spokes of a bike, except more violent because its not a card making the noise.

Regular driving doesn't make the sound, the only reason I even noticed it was because I had it in for a belt tensioner replacement and the dealership told me I needed a new engine ($5700).