strange noise from drive shaft(s)?

just started hearing this noise and have narrowed it down to under the vehicle.
noise sounds like a high pitched squealing and only happens while in drive or reverse. when in neutral the noise goes away, so I do not think it is the brakes.
I checked all the fluid levels tranny, oil, transfer case, diffs, etc. I greased the fittings I could find, but still have the noise.
Anyone have any suggestions as to what or where else to look I would appreciate it!

Thank you

i just started my car and it was doin that too it was a high pitched eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee yeah its annoying but it almost sounds like its coming from my fan or something. maybe i dont know

I do not think it is engine related for this reason;
1) only does it when in drive or reverse
2) rev engine in park or neutral and no noise
3) while driving and noise happening, throw it in neutral and noise almost gone(this might rule out drive shafts as they are still turning)
4) noise increases with rpm increase

ohh well then i dont know mine makes the noise when i start my xj and does it whether im driving or parked but it doesnt get louder or anything when im driving so i dont know it kinda just stays consitsant, whenever i wash my car and engine it goes away though.

So the noise increases pitch with increases in vehicle speed? Could you describe it as "angry sparrows"? when you're moving? If so, it's almost surely the centering joint in the front driveshaft.

Jim