Help! My Truck Sounds Like It Has A Turbo!

[00Buckshot]

Ok, so... I need help...

I have a 96 Explorer 4.0L OHV 4x4
The engine light is NOT on... so there are no codes showing.
When I hit 2nd gear, my truck whistles like I have a Turbo installed in it!
But this does not occur in 1st gear, and only occasionally in 3rd... Never at the same RPM tho :scratch:
My milage SUCKS! I am getting about 200 KM to a full tank of fuel. :fire:
Keeping in mind I only paid $200 for it... but even still.. I am kind of stuck on what the problem is. I have searched for a loose/missing vacuum line, but could not find one..
Any other ideas out in the Explorer World??
I would love some advice on this issue!

Thanks!

 

[Runnin'OnEmpty]

Welcome.

The problem might be one of several things, but first
check the vapor hose that runs from the bottom of the
throttle body to an emissions valve on the driver's side.

These split/crack/deteriorate and could cause a
whistling noise...

 

[Robman]

could it be the trans ? It's automatic yes?