When I put my truck in 4x4 it works great, but once I go back to 2x4 it makes a high pitch noise when I drive. Almost like a stick hitting the spokes of a bicycle, but a whole lot faster. But once I get on the accelerator and the engine downshifts and starts going the noise stops and everything is back to normal.
Does anybody have a suggestion about what it is and if its bad for the 4x4 components in general?

 

sounds like you have a vacuum leak or bad IWEs... search "IWE" and you will find tons of info on here

 

Thanks man!

 

you're welcome