It's a 2002 Silverado bought new, small v-8 and manual transmission. The rear seal was replaced recently and differential fluid is full. Anyway the whine seems to be getting louder by the day no matter if the clutch is in or out or at what speed.
Does the whine happen at idle in neutral?
If it is whining at idle and not moving remove the fan belts and see if the noise goes away.
This can help eliminate the alternator, power steering pump, A/C compressor and any other idler pulley that may be in the system.
Let me know if this works. If the belts are off and you still have the noise then let me know we can diagnosis the noise further. Try to give me as much detailed information you can, this helps me get a better picture of what is happening.