Loud squeal under load

[c33733]

Hi, First post here. Hope someone can help.
Have a 05 Explorer Eddie Bauer V8. 160K miles.

There is a very loud squeal under load. Sounds like a slipping belt, everyone that hears it at first says the belt needs to be replaced.
Bought car in October '13. Noise appeared about 5 weeks after purchasing car. Definitely was not there when bought.
It is definitely coming from the engine area, hard to tell exactly as it is only heard when driving and my head can only stick out the window so far.
It will not make the noise when stationary in neutral or park at any RPM or short on off rpm bursts.
It will make the noise under load at any speed, not at any specific RPM's but always around 2K 2.5K and above under load.
The noise gets higher pitched as the revs increase under mild to hard acceleration, but with gas off to cruise, goes away.
It does this from cold (doesn't change when hot).
I have checked the belt and bearings, but the noise is still there even with the belt completely removed, so that eliminates those.
Driven with air box open to eliminate bad seal.
Checked for vacuum leaks, found one and fixed.
Needed a coil pack replaced on #5 but the squeal was there before that went bad, so I guess just coincidence.
Replaced right front wheel bearing that hilariously wasn't noticeable on test drive and developed shorty after buying.
Checked for exhaust leaks.
No computer codes apart from random misfire and misfire #5 which was fixed with coil replacement.
There is a small hesitation from stand still and gas pedal is touchy from stop, but have been told that is normal.

That's about it. Makes me wonder why the previous owner sold it but honestly it seemed fine when I bought it. Bought it from a car dealer as is.
Thanks!
Cameron

 

[Limited02]

If you have the tow package, then you will have the 3.73 limited slip rearend. It is VERY common for it to create a high pitched whine in the manner you describe. Take it for a spin and when you clearly hear the whine, let off the gas. Normally you say it goes away? Now give it just enough gas to barely gain speed. Does the sound come back?

 

[c33733]

Thank you for your reply. I appreciate it.
I assume it has the tow package as it has a tow bar. Yes it always goes away as you describe and comes back with little gas. The only extra info to this is that the faster I go the more gas it takes to squeal. Cruising at 60mph then it almost kicks down first, squeals then kicks down and squeals at higher pitch with the revs. Slower and the less gas it takes.