About 2 months ago my trucks power steering pump went out, I replaced that and everything was all good again... about a month later I start to get this weird sound. It sounds exactly Like a supercharger (There is no supercharger on this truck) Its just a faint whine that is linked to the RPM's. It is not the Power Steering pump because it does not change at full lock and I have replaced both the pump and pulley for a 2nd time because I though it was makeing the noise. Any Ideas? It echos throughout the engine bay so its almost impossible to pin point.

 

get a garden sprayer with a long squirter wand and spray water on the pulleys one at a time. Sometimes the sound goes away when wet. That is how I've found noise sources in the past.

 

Possibly a dry bearing on a pulley tensioner.

 

Could be the alternator. They are known to produce a whine like you describe. Put your hand on the alternator (CAREFULLY!!) while someone revs the engine a bit and you will likely be able to feel the noise you are hearing.

 

I'd recommend getting a mechanic's stethoscope with a long probe and probe each bearing on the engine front (the long probe still conducts sound very well but will save your fingers from the fan).

In the past, I've used long pieces of hose or a piece of wood dowel with a cup on the end for your ear, but the stethoscopes are very cheap these days and a lot easier to use.