I have an 92 240 wagon

it started making a strange whining noise when running at 50 mph and above after driving 5 minutes or so. It is not a grinding noise like a bearing or brake pad. It is not the hum from a fuel pump
issue. It is not the squeal of a belt slipping. It is more like an
electric whine that comes from the front of the passenger side. kind of like flying in a jet plane when decelerating or
a small electric motor spinning up to
high rpms until it gets to a steady high pitched whine. Then if I let
off the gas, it sounds like it is spinning down. When I try
revving the engine, while parked, to an equivalent rmp I do not get
the sound. I'm sure it's not the fuel pumps because I've just
replaced both and am very familiar with the pump noise. I'm also
familiar with belt squeals, brakes grinding and bearing noise and
that's not the type of noise I'm hearing.
Can it possibly be related to a service belt accessory bearing from not having the underpin under the bottom front since like many others was too lazy to put it back on? Some are mentioning the carrier belt on drive shaft but how can I be certain and what are the other symptoms? Sorry for so many questions and thank you for your help.

This is stumping me so any help will be appreciated.