Blazer S10 issue with whining/loud reving sound

On cold engine, remove serpentine belt and run engine for a few seconds if noise goes away, then accy drive like belt tensioner.

If not, then possible transmission problem.

You need to make sure this is actually the engine. Because if it was, it should make this noise anytime engine rpm increases, in park or drive.

So do you hear this noise while the car is moving only??? (If your car is in drive, but foot on the brake, do you hear the noise???)

Does the noise increase with speed?

Sometimes the powersteering pump will make this noise when there's a load placed on it. If it were the water pump, alternator it would make this noise no matter in park or drive. Your a/c compressor would only make a noise when it's turned on.

Keep in mind, a bad hub/wheel bearing makes this noise as vehicle speed increases and sounds as if it's the engine/tranny. Are you sure it's not that?

Removing the belt is simplest method to eliminate assy drive component.

From what you said it sounds like it makes noise whenever engine is revved, even in Park?

You said you don't hear the noise when in Park or Nuetral. The only way this could be your engine accy is if it's the power steering pump, and that would only make the noise while under load.

You can remove the belt and start the engine and reproduce the same conditions that gave you the noise at first. If it goes away, then it's one of the accessories. If it persist, then look for something other than the engine. (Don't drive the car long without the belt on. A couple minutes at most)