1998 Jimmy Transmission

[98jimmy]

I noticed when I place the Jimmy in drive or reverse I hear a whining noise. I ask a know GM mechanic to listen to it. He thought that the pump was straining to pump the oil. Suggested to replace the filter first. This was done and needed to be done. But the oil pump seem to have plenty of pressure, hence the line to the radiator was taken off to drain the oil. The whining was still there, What else might it be?